I’ve noticed something in particular this season down on the farm for the Seattle Mariners. Before players are promoted, they’ve performed at a high level for an extended period of time.

While that may not sound especially notable, it is in this context: Previous regimes promoted players despite showing at the lower level they had a ways to go. Matt Tuiasosopo and Mike Zunino are two that stand out among a long list.

And I don’t just mean statistically. There are times the numbers may not look great but the player has shown he’s ready for more. Conversely, there are times the numbers, at least some of them, look good, yet others don’t and the aggressive developmental approach backfires.

The current player development formula in Seattle seems to cover all the bases, and errs on the cautious side, if anything, despite the fact we’ve seen young-for-the-level players promoted.

Among the many oddities in the minors that may confuse fans when looking at numbers comes with the difference in hitting approaches down in rookie ball or even some in Low-A, versus the higher levels.

Kids in the lowest levels tend to struggle versus offspeed stuff so they don’t swing at it much, hoping it’s out of the zone. Pitchers, also of the lesser-experienced variety, often don’t command their offspeed stuff as well, so the result often is a pitcher with lackluster overall statistics, despite acceptable or even very strong execution. And for pitcher who do locate well, they throw a lot of breaking balls out of the zone on purpose, because that’s what you do to get swings and misses, but instead end up falling behind in counts or allowing hitters back into them, despite executing perfectly.

In High-A or Double-A, hitters can handle more of the offspeed stuff, and know if they just take those pitches pitchers will dominate them.

Why does this matter? Statistics don’t tell the development story many think they do.

Julio Rodriguez, OF
Rodriguez’s season has included two breaks to play for his home country in the Olympics, but there is nothing about his performance to suggest he’s been distracted.

He’s not hitting for a ton of power, but that appears to be more of a sign of maturity than anything else; he’s not being given a lot to hit, and it taking the singles and walks and not trying to pull or lift everything.

Rodriguez has clearly been focused on swinging at strikes and hitting the ball hard without too much specific intent. The result has been a lot of hard-hit balls from line to line, and a hit-over-power game plan that’s working.

The long balls will come more naturally, and that’s an offensive advantage Rodriguez has always had over everyone else in the system. He has his own mechanical tweaks to make, however, which is why it’s not surprising at all the Mariners didn’t ship their top prospect to Triple-A or even the big leagues.

He’s still an above-average runner who gets out of the box quickly, especially for a bigger player with 70 raw power. He’s also still just 20 years of age, suggesting as he continues to fill out physically, he’ll lose a half step or so and land in the average range in terms of foot speed, and outfield range. He’s shown very good baserunning instincts, including an ability to take advantage of minor league batteries.

The arm is plus to plus-plus, and Rodriguez has cleaned up a lot of loose ends — hitting the cutoff man, throwing to the right base, not taking chances in key situations, et al — since his days in the DSL.

In August, Rodriguez played just 15 games for Double-A Arkansas, but batted .407/.529/.519. He walked 13 times and struck out on just six occasions in nearly 70 plate appearances.

He’s among the best prospects in baseball and on a journey that certainly lands him in the majors sometime in 2022.

The Franchise is coming, folks.

George Kirby, RHP
Kirby has been outstanding in 2021, and while his August in Arkansas consisted of three shorter starts (by design), one of them turning up lame (4 ER, 3 BB, 1 IP), I’ll reiterate my comments on Twitter from last month: Kirby is a better pitching prospect right now than Logan Gilbert ever was, and Gilbert was pretty good and has bright future ahead of him.


Kirby is 94-98 every time out and always touches the upper range, and has two legit breaking balls led by a plus slider. His changeup is already useful and flashes average, and his general control is plus.

Despite not being quite the phenom prospect King Felix was, Kirby is in Felix territory in one aspect: From here on out it’s really as simple as watering him and watching him grow. He’s on the path.

For the season, Kirby has made 13 starts and covered 57 innings. He’s allowed 46 hits, walked 12 batters and struck out 70.

He’s RP1 in the system right now, carrying No. 2 upside and a high mid-rotation floor, likely seeing the majors sometime next season and sticking in 2023.

Noelvi Marte, SS
I’m still firmly on the ‘3B’ side of Marte’s ultimate defensive landing spot, but one significant piece of info I’m taking from his defensive development is the simple fact he worked very hard at it and got a lot better.

Playing on the dirt, whether it be at third or short, requires a lot of the same skills; lateral movement, arm strength and accuracy, quick release, clean transfers, throwing off balance. Showing he can do a lot of that and eliminate mistakes is enormous.

Marte had a tough July at the plate — .219/.270/.316 — but rebounded in August, batting .287/.412/.553 with 18 walks and 19 strikeouts in 115 PAs.

For the season he’s at .271/.368/.462, and will not turn 20 years of age until October 16.

He’ll get a few weeks in Everett to complete his season and likely start there next April. His timeline hasn’t necessarily changed as a result of his performance this season, mostly because it was difficult to place one on him after no 2020 and only seeing the stat line from the DSL in 2019.

He’s acclimated very well and is now getting some Manny Machado comps as he’s grown and filled out, and it’s not as crazy as some might think.

The power is legitimate 65 raw, and he’s showing developing tools that allow him to hit with increasing consistency.  The adjustments he made this summer bode well for his future.

If you’re an opposing pitcher that’s in or will eventually land in the High-A West league, here’s some advice: Tread carefully.

Matt Brash, RHP
We’ve talked a lot about Brash on Baseball Things, and he’s a constant topic on Twitter, and that’s because despite his lack of prototypical size (6-1, 180), and despite the concerns about the delivery, he’s done nothing but dominate all season.

In fact, Brash, 23, has been better in eight starts at Double-A Arkansas than in 10 outings for High-A Everett. Since the promotion, he’s logged 44 innings and allowed just eight earned runs on 22 hits. He’s walked 16 — which is a little high — but he’s punched out 69 batters.

For the year, Brash has 131 strikeouts in 86.1 innings — 37% of batters faced.

He will lose his release point occasionally, explaining the walks and the good-not-great 62% strike rate, but he’s been nearly unhittable at times and has the best present stuff of any arm in the organization, including the big leagues.

The fastball is firmly 94-98 mph with run and ride and some deception thanks to his bend and three-quarter arm slot.  His slider is just pure filth with late two-plane break, and it appears he either varies the velo on it or throws an actual curveball that he can throw for strikes, too.

His changeup is inconsistent, but far from a project pitch; in his August 19 outing when he no-hit Frisco for 6.1 innings and fanned 11 in seven frames, he threw a handful of projectable changeups with some arm side run and sink, and let me explain something here: In any role, if Brash is 94-98 with a 65 slider and either an average curveball or changeup, he’s going to beat good lineups. If he has both of the latter pair, he’s going to destroy them.

Brash made four starts in August, allowing three earned runs in 23.1 innings. He walked nine and struck out 37.

He’ll need to clean up the spotty control, but the stuff is flat out wicked and rivals that of anyone else in all of the minors. If he can find a way to stay in the rotation, I don’t know what the right ceiling projection is, but I lean No. 1. There’s just more risk here than with some of the other arms in the system, so until he answers those questions he’ll be ranked a little lower than Kirby, Emerson Hancock for me.

Brandon Williamson, LHP
Williamson has had a very good year and was the first of the arms to move from High-A to Double-A. He’s thrown strikes fairly consistently all season (64% strikes thrown, 32 walks in 87 innings), and his stuff has improved across the board.

His difference maker is the fastball, with deception and high spin, he generates swings and misses 91-94 mph. But at times in his amateur and pro career, the left-hander has flashed 95-97 mph heat, and anywhere 94-plus the pitch has been devastating to minor league bats.

His slider has proven a real weapon versus lefties this season and he’s shown enough with the changeup to maintain legitimate four-pitch status. His curveball is plus at times, landing firmly in the above-average range, and can be used effectively versus both lefties and righties, and in any count thanks to good command.

I don’t see a frontline ceiling unless the velocity ticks up and is consistently 94-plus, but there’s a quality mid-rotation arm here that is still developing from stuff to command, and it’s impossible not to like the foundation he’s built on deception, fastball value, and pitch mix.

Williamson was dirty in August, logging 20.2 innings and yielding just three earned runs on eight hits. He posted a 34-9 K/BB ratio in four starts.

There certainly is a chance he hits the majors next season, but I don’t think he’s on the fast track, and I don’t think he’s an ideal candidate to transition into the majors through a relief-first path, which theoretically gets arms to the majors quicker, at least in many cases.

Connor Phillips, RHP
Phillips is a legitimate prospect on the mound being underrated by many in the industry. Kudos to Seattle for seeing the upside on him in last year’s draft and taking the chance he can start or develop into a high-leverage reliever.

The raw stuff is undeniable, starting with a fastball into the 95-99 mph range, showing life up in the zone and some run in on right-handed batters. He has two breaking balls, the best of which is a slider that has flashed plus and more typically dwells in the average to above-average range. But it’s projectable and potentially a true strikeout pitch for the right-hander, who pairs the pitch with his four-seamer very well.

He added a curveball, a relatively new pitch for him, and it flashes some promise but needs to be sharper, and his changeup remains below average but occasionally looks more than useful for him.

There’s a legit chance at a three-pitch mix here, and four isn’t out of the realm of legitimate possibility. What is in question is his control and command.

Phillips has issued 44 walks in 72 inning, and the contact data on his stuff strongly suggests throwing more strikes will benefit him greatly, even more than most arms. He’s allowed the least barrels among any pitcher in the Low-A circuit, minimum 50 innings pitched, and just one home run in 322 batters faced. Opponents have slugged just .288 off him this season.

He’s a physical arm, listed at 6-foot-2 and 190 pounds but looks more like 215, and there’s above-average athleticism, lending confidence he can fine-tune his mechanics and throw more strikes.

Starters that can pitch effectively in the zone have an advantage over those that cannot, and Phillips may be one of those thanks to his fastball, both in terms of velocity and movement, and he’s had 14 or more whiffs in a game five times, including 17 in his last outing and 22 back in May.

Best part about Phillips’ development is this is just Year 1, and he won’t turn 21 years of age until May.

Milkar Perez, 3B
Perez, who was just promoted to Low-A Modesto, is a bat-first, fringe-defender listed as a third baseman, but his profile is led by above-average raw power that projects to grow as he does.

Thus far he has shown a solid line-drive swing, but he has expanded the zone a little often and his contact rates suffered a bit as a result, but has a track record of avoiding the chase. He’s just 19 — he’s exactly the same age as Marte, down to the day — and hit for average in the rookie league, but 10 doubles and a sub-.400 slugging percentage is all he has to show in the power department.

If Perez can’t stick at third base, power is going to have to be a big part of his game or at this stage of his experience I wouldn’t think much of his zero home runs in 145 at-bats.

I do wonder if moving to right field is a possibility; He’s not a great athlete but has a terrific arm and if he has issues managing at the hot corner, right would seem like a spot to at least consider, even with a lack of foot speed.

Either way he’s a bat that needs to rake pretty big to play regularly, but I’ve seen 10-15 home run projections on him that I think should be ignored. There’s bat speed to back up more than that, he just needs to develop the kind of swing that to get to it and that takes time.

Perez’s .313/.430/.391 slash in August was noteworthy, and now we’ll get to see him give the former Cal League a go.

Alberto Rodriguez, OF
Rodriguez, the return for Taijuan Walker last summer from the Toronto Blue Jays, struggled for the first 5-6 weeks of the season, but since June 17 went .343/.400/.547 with 24 doubles, three triples, and eight homers.

Lots of barrel and a strikeout rate under 18% over that span, too. No wonder the club thought Everett was where he should end the season.

He’s a sturdily-built left-handed stick with above-average raw power and hit tools. He throws pretty well and has average range, but is limited to a corner spot. The Mariners like the bat speed and bat-to-ball skills and so far Rodriguez is rewarding them.

He’s 21 in October and has a shot to reach Double-A next summer. He worked to get into better shape after last season and more of that is probably needed if he wants a chance to play everyday.

Starlin Aguilar, 3B
Aguilar has played 35 games down in the Dominican Summer League, looking a lot like Perez, with whom he shared a lot of similarities, both physically and in terms of tools.

Aguilar, however, has a raw power advantage, and therefore an upside advantage, too. But there’s as much or risk in his profile because of the lack of full confidence he sticks at third base long-term, hence the chance he’s a bat without a position.

But the scouting report also suggests a better-than-Perez chance he hits enough for first base, so while he comes with a little more risk right now, the upside evens out the comparison between the two, which is how I’ve been ranking them.

Edryn Rodriguez, 2B
Rodriguez is not a name that gets much play because he wasn’t one of the bigger signings. But he has been one of the better performance this summer in the DSL. He hit .296/.415/.537 in August and has fared well enough at second base defensively to leave him there and see what happens.

He’s not a great athlete but a solid one, and if he has to move to left field it puts more pressure on his bat, but despite his lack of stature — listed at 5-9, 150 pounds, though these sizes are often off 5-15% in weight — he’s finding the barrel a lot and has a chance for average power.

Rodriguez is just 18 with hopes to crack the ACL or better next season, thanks to a very strong performance with the bat in 2021.

Tyler Driver, RHP
Driver, 20, has pitched at three stops this season, mostly in rookie ball after being the club’s 18th-round pick in 2019. He’s a right-hander out of Cary, North Carolina who has worked a ton on adding strength to his 6-foot-2 frame. He’s still listed at 185, but appears to have creeped closer to 200, and after some uneven outings in the rookie league has shown out a few times of late.

Perhaps one of the victims of what I discussed in the lede regarding breaking balls and inexperience hitters, Driver’s numbers were uninspiring in Arizona, despite four scoreless multi-inning efforts with clean lines, and more strikeouts than innings pitched.

But in a spot start in place of Levi Stoudt in Double-A Arkansas on a day he arrived just hours before game time, Driver put together his best professional start.

He went six innings, allowing six hits and an earned run, walking one and striking out seven. His fastball is low 90s, but he mixes in a lot of two-seamers with above-average run and some sink, and a changeup that pairs with it very well. His slider is above-average and works off either of the first two pitches.

I’m not sure what Driver is moving forward, but he’s taken the developmental approach to his career, which bodes well for the end-result, and his pitchability and improved stuff suggest a big-league profile of some sort. And Driver, in many circles, is just an org arm, and I get that assessment of him. He’s just betting on himself with work, and the physical tools and pitches are there to outperform that eval.

Arms grow on trees in this organization, it seems.

NEW: Top 5

It’s the final monthly prospect report of the season, but I thought it’d be a good time to unveil a new part of this piece, which will continue next season. A top 5.

It can be anything from Top 5 at a position group, top 5 of a specific tool, top 5 performance, whatever jumps out at me for the month.

This month: Top 5 pure relievers in the farm system.

By pure reliever I mean an arm either currently pitching in the role that isn’t being developed as a starter, or a recent draftee with heavy expectations a relief role is his future.

5. Luis Curvelo, RHP
Curvelo, 20, is into the upper 90s with an average to above-average slider, and has posted 74 strikeouts and 17 walks in 51.1 innings this season, his first in full-season ball.
4. Ray Kerr, LHP
Kerr is 95-100 mph, and occasionally has hit 102, setting up an above-average slider. He’s athletic, repeats his delivery, and is throwing more strikes than ever since his promotion to Triple-A Tacoma last month. Expect Kerr to be at least a fringe piece of the bullpen conversation in spring training, and one of the first call-ups during the season.
3. Yohan Ramirez, RHP
Ramirez is still more than 10 innings from prospect graduation, but he may be turning a corner when it comes to harnessing his plus stuff. More strikes, fewer walks, similar strikeout rates, and it’s all adding up to more success in the majors.
2. Bryan Woo, RHP
Woo, who had UCL surgery and won’t pitch until mid-to-late 2022, has been up to 98 mp with a plus breaker, and projects as a potential back-end bullpen arm. He threw strikes at Cal Poly — 15 walks in his final 45 innings, and just eight in his 28 frames in 2021 — to suggest effective control in short stints.
1. Andres Munoz, RHP
Velocity is a big part of Munoz’s game. He’s been up to 104 mph and regularly sat 99-101 in his big-league stint before falling to elbow surgery.

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Jason A. Churchill

Churchill founded Prospect Insider in 2006 and spent several years covering prep, college and pro sports for various newspapers, including The News Tribune and Seattle PI. Jason spent 4 1/2 years at ESPN and two years at CBS Radio. He now serves as the Executive Copy Editor at Data Skrive, a tech company that manipulates data to provide automated content to clients including the AP, BetMGM, USA Today, and ESPN. Find Jason's baseball podcast, Baseball Things, right here.


  1. Love this

  2. So good. Thank you.

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