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The Filthiest Pitches in the Mariners Organization


TrackMan, Rapsodo, and HawkEye have permanently, impenitently changed the game. Sometimes it feels like decades have passed since the eye test was the an acceptable applied means of quantifying a player’s ability on the field. The advent and indoctrination of spin rates, spin axis, spin plane and release point have empirically changed the way folks view baseball. It’s a granular game now, overthrown by science, physics, calculus and the unending pursuit of a marginal advantage.

That frivolous clout can be found buried in the numbers -- not necessarily the numbers in the box score, but the underlying numbers from every individual sequence on the field. Every pitch has a fingerprint, each different than the last. It’s the aggregate mean of those pitches as a whole that shows who’s truly special.

Welcome to 2020 and player development.

Just as velocity could single-handedly get you a hefty signing bonus in 2010, so too can spin rate in 2020. A violent curveball with extreme tilt will have scouts salivating just as a 98 mile per hour heater will. Profound breaking balls that show consistent tilt and can be thrown for a strikes are the new currency in Major League Baseball and the Seattle Mariners have a few dandies.

In this piece, we’ll examine the cream of the crop in the Mariners organization. From velocity to spin rate, as well as horizontal and vertical break, let’s dive into who truly has the nastiest stuff on the farm, and who we can expect to have a breakthrough in 2020.

Now to qualify for this list, a player must still have prospect status. Austin Adams, for example, has one of the most lethal sliders in the entire sport, but for this exercise we’ll withhold his name from consideration. These are the guys that may be on the precipice of seeing time with the big league ball club, and furthermore, opening a lot of eyes along the way.

The numbers provided in every case will be an average from every single pitch thrown during the 2019 season. These won’t be peaks or valleys. No biases toward either end of the spectrum.

Let’s start from the top. Here are the Mariners’ hardest throwers, as well as where they’d rank among the best in Major League Baseball, according to Statcast.

4-Seam Fastball


  1. Gerson Bautista - 98.1 mph - 99th percentile
  2. Connor Sadzeck - 96.5 mph - 91st percentile
  3. Jake Haberer - 95.6 mph - 82nd percentile
  4. Art Warren - 95.4 mph - 81st percentile
  5. George Kiby - 95.1 mph - 77th percentile

Kirby may be the surprise here. Lauded for his plus-plus command, the Elon product can certainly bring the heat, topping out at 98 mph in Everett. Warren is already well-known for his fastball and should see extended time in Seattle next season. Haberer on the other hand isn’t as familiar a name to most Mariner fans. An undrafted free agent out of Eastern Illinois, the right-handed reliever has moved quickly through the organization, pitching across three levels in 2019. Walks have been a small issue thus far, but Haberer has two more controllable years to hone it in.

But as was mentioned above, it’s not all about velocity. Some of the best fastballs in the league don’t top 95 mph. When you have late ride and deception, a good fastball can be almost un-hittable.

Spin Rate:

  1. Dayeison Arias - 2541 RPMs - 96th percentile
  2. Joey Gerber - 2536 RPMs - 96th percentile
  3. Brandan McGuigan - 2516 RPMs - 94th percentile
  4. Elvis Alvarado - 2507 RPMs - 94th percentile
  5. Kyle Wilcox - 2477 RPMs - 92nd percentile

As is clear, Seattle has some guys in the organization with some real funk on their heaters. Arias was a rising star last season, posting a 1.15 ERA across West Virginia and Modesto. 80 strikeouts in 55 innings is nothing to scoff at, giving him serious helium headed into 2020. More and more, Arias is looking like a future high-leverage guy, and possible closer for Seattle. Since being drafted in 2018, Gerber has been tabbed as a fast-mover in the bullpen. He brings a ton of deception to the mound with an unorthodox delivery and will likely see time in Seattle in 2020. His stuff, and I can’t stress this enough, is cartoony. McGuigan was an undrafted independent ball signee who just completed his first season in West Virginia. Alvarado was acquired from the Washington Nationals in the Strickland/Elias trades last season -- he’s a few years away. Wilcox has been with the organization for five years now, though he’s really starting to find his stride the last two seasons. He’ll get a heavy dose of AA in 2020.


For the slider, we’re going to evaluate the pitch a little differently. Velocity is obviously great when it comes to breaking balls, but spin rate and horizontal break are probably more important in the success rate of the pitch. For the crowd clamoring for velocity numbers, Sadzeck leads the organization at 89.4, while Wilcox follows a healthy distance behind at 88.3. Also, to get the cat out of the bag, yes, Adams has the most elite slider in the organization at 2836 RPMs.

Spin Rate:

  1. Ben Onyshko - 2834 RPMs - 95th percentile
  2. Brendan McGuigan - 2821 RPMs - 94th percentile
  3. Bernie Martinez - 2796 RPMs - 93rd percentile
  4. Sam Delaplane - 2788 RPMs - 93rd percentile
  5. Brandon Williamson - 2684 RPMs - 87th percentile

A 24th round pick out of Stetson, Onyshko was overshadowed by teammate Logan Gilbert leading up to the draft. A southpaw, Onyshko spent his entire 2019 at West Virginia, posting a 3.99 ERA over 71 innings. Martinez is yet another undrafted free agent the Mariners have had success with. Having pitched 43 innings across four(!) levels in 2019, Martinez topped out at AA Arkansas last season. Barely 23, Martinez has tons of time to develop with the organization. Delaplane is a name many will recognize. A 2017 23rd round pick, the Eastern Michigan product has been nothing short of extraordinary the last two seasons, striking out 220 batters over 127 innings. He’s on the cusp of a big league debut.

The more scouts, coaches and talent evaluators I’ve talked to, the more people should be keeping an eye on Brandon Williamson. Thought to be more of an under-slot signing, many now believe Williamson could end up in top 100 lists by this July. One evaluator said he expects the 6-foot-6 lefty to be a top 5 prospect in the Mariners organization by that time, which is saying a lot. He got hit around a bit at TCU, but upon arriving at short-season Everett last season, it became clear Williamson’s stuff was far better than anticipated. As long as the body can stay healthy, watch out for Williamson who figures to start 2020 at High-A Modesto.

Horizontal Break:

  1. Benjamin Onyshko - 14.8 inches - 99th percentile
  2. Brandon Williamson - 13.4 inches - 99th percentile
  3. Justin Dunn - 10.5 inches - 90th percentile
  4. Logan Gilbert - 10.1 inches - 90th percentile
  5. Jarod Bayless - 10 inches - 90th percentile

Now, let’s talk about the elephant in the room. How can these guys have such elite horizontal movement on a slider, but not be scouted as having 60-grade sliders? Some of it has to do with vertical drop, late life, how it plays off the fastball, deception, etc...

That being said, several scouts would indeed rate Williamson, Dunn, and Gilbert’s sliders as 60-grade plus pitches. Horizontal movement is just one slice of the pie. If you can throw it for strikes, it’ll set you apart from the crowd.

Onyshko’s slider, yet again, sees itself atop the leaderboard. The slider, if we’re being fair, is more of a slurve with serious loop. It presents itself more like a slurve to hitters, but I can confirm it is a slider grip and slider mentality. A high-70s/low 80s breaking ball can only get so tight and stiff, thus the current shape Onyshko is able to present. The reason he isn’t higher on most prospect boards is the fastball. At just 88 mph, and it’s a non-lethal pitch. Well below average spin on the pitch adds to the issue. That being said, he just finished up Gas Camp two weeks ago, so an Ljay Newsome-esque ascent in 2020 isn’t out of the question. With one of the more promising breaking balls in the organization, he clearly has a pillar to build upon.


The curveball is a tricky pitch to analyze without providing mind-numbing amounts of data. Every pitch is different. Some have 12-6 tilt, while others have more of a slurvy 2:00 tilt. The axis upon which a pitch rotates is unique to the pitcher throwing it. Horizontal AND vertical movement play a massive role in this pitch. We’ll examine spin rate, of course, but instead of doing a top five, we’ll take a different approach.

Spin Rate:

  1. Anthony Misiewicz - 2857 RPMs - 90th percentile
  2. Art Warren - 2768 RPMs - 82nd percentile
  3. Anderson Mercedes - 2691 RPMs - 84th percentile
  4. Brandon Williamson - 2686 RPMs - 84th percentile
  5. Jorge Benitez - 2682 RPMs - 84th percentile

Misiewicz makes his debut on the list having the best yacker, by spin rate that is, on the farm. Seattle drafted the former Michigan State Spartan in 2015, and have since traded him to, and acquired him from, the Tampa Bay Rays. At this stage, Misiewicz appears more primed to be a spot starter/quad-A guy than a consistent option at the big league level. He’s been hit around pretty good the last three seasons across AA and AAA. Warren’s curveball is devastating as it plays really, really well off his high-90s fastball. Mercedes is yet to throw in full season ball, and the results haven’t been great just yet, but at 20 years old, he’s got plenty of time to find it. Williamson once again receives high marks for an above average breaking ball. Throwing his curveball for strikes is the last test necessary to graduate the pitch into a 55-grade weapon. He does a great job of repeating arm slots, even for a guy his size. Benitez was a 9th round selection in 2017 and has impressed in his three seasons with Seattle, though he is also yet to pitch in full season ball.


For this, we’re simply going to highlight some standouts

  1. Jarod Bayless - 13.3 inches induced horizontal break
  2. Art Warren - 12.5 inches induced vertical drop
  3. Jorge Benitez - 12.4 inches induced horizontal break
  4. Evan Johnson - 12.3 inches induced vertical drop
  5. George Kirby - 12 inches induced vertical drop
  6. Brandon Williamson - 11.9 inches induced horizontal break

Warren, Benitez and Williamson pair their strong spin rates with excellent break to match. Kirby and his 1:00-7:00 bender play better than even these numbers show as he throws the pitch consistently for strikes. He’s been known to happily throw it on full counts. At the end of the day, the ability to throw the curve for a strikes can make or break its effectiveness.


The changeup is so incumbent upon release point, arm action, command and the fastball that Trackman data really doesn’t tell the whole story. That being said, whether the pitch vertically dives at the plate can be the difference between it being just “a pitch” and it being a weapon. Marco Gonzalez has the best changeup in the organization, getting over a foot of vertically induced break. To qualify, a pitcher had to have thrown at least 50 changeups this season.

Vertically Induced Break:

  1. Tyler Driver - 13.3 inches
  2. Ryne Inman - 12.8 inches
  3. Deivy Florido - 12.4 inches
  4. Erik Swanson - 12.3 inches
  5. Sal Biasi - 12.2 inches

Driver, 18, was an 18th round pick by the Mariners in the 2019 draft. He’s got a good frame at 6-foot-2 and is still growing. The fastball shows good life, but only lives around 88 mph. If he can improve that into the low 90s consistently, Driver will be a name to keep an eye on. Inman has been with the organization for five years now, having started 25 and 26 games in the low minors the last two seasons. Florido, 19, was an international signee two years ago and got his first taste of stateside baseball this season. He’s likely to start 2020 at West Virginia. Swanson is a known commodity who uses his changeup to play off an elevated fastball. He’s likely to start 2020 in Tacoma and will used in long relief. Biasi was acquired for catcher David Freitas in the first couple weeks of the 2019 season. He was thought to be a potential fast-mover in the bullpen, but scuffled at low-A West Virginia.

It should be noted that zero Trackman data was available for Sam Carlson as he didn’t throw in any games this season. His changeup is considered a plus, 60-grade offering and will surely be something to watch for in 2020 as he works his way back from Tommy John surgery.

At the end of the day, all this data does is help flash potential. You can spin the ball better than anyone in the world, but if you can’t find the strike zone, or sequence pitches to keep batters off-balance, it just won’t work. It’s especially exciting to see names like Dunn, Gilbert, Williamson, Warren, Arias and Delaplane (among others) on this list as, in a sense, it validates they have the stuff to succeed at the highest level.