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Sidewinder missile: Mariners prospect Wyatt Mills is moving quickly through the system

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The fastest-moving arm in the system comes at you sideways

(Kevin Clark / The Herald)

As we enter the fourth week of the 2018 MLB season, the Mariners’ pitching staff finds itself somewhere in the bottom third in most categories. That holds true for their bullpen, which currently sits 23rd in the league in xFIP with a mark of 4.33, and tied for 27th in fWAR at -0.3. Other than closer Edwin Diaz, who has been absolutely lights out in 10 appearances, the bullpen has combined for -0.8 fWAR (or just -0.7 if you omit Taylor Motter’s appearance in a blowout). The team’s prized free agent acquisition Juan Nicasio has looked far from the pitcher he was last year, as he’s dealt with home run issues and decreased velocity here in the early going that have paved the path to a -0.3 fWAR.

Outside of Chasen Bradford, acquired off waivers from the Mets, the ‘pen as it stands now is returning Marc Rzepczynski as the only reliever from last year’s unit to post a GB% < 40%. Bradford currently has a GB% of 63.3%, but as one of the relievers with minor league options, it seems likely that Chasen will be riding the Tacoma-to-Seattle express a few times as the Mariners juggle their roster into the summer [angry hissing noises]. Barring the revelation of a nagging injury, we can expect Nicasio’s GB% to eventually climb back north of 40%, where it’s sat for his entire career, but it currently stands at 27.6%. The loss of sidewinder Steve Cishek--whose 56.1% ground ball rate was second to Rzep’s--in particular stings for the team’s relief corps. Wouldn’t it be convenient if we could find another one of those somewhere…?

Enter Wyatt Mills. Mills, who the Mariners made the 93rd overall pick in last June’s MLB Draft, has been moving quickly through the organization, as he’s already been promoted twice following stints of 7.0 and 13.1 innings pitched. Like Cishek, Mills comes at hitters with a true sidearm delivery, something he picked up following his freshman season at Gonzaga University. He mentioned it as something he developed in an attempt to give him to separate himself from all the other right-handed relievers who throw *only* 85-88mph across the nation, as he did at the time.

Also like Cishek, Mills has demonstrated a keen ability to generate ground balls throughout his professional career. Now with his third affiliate since joining the organization, he’s posted a ground ball rate of 50% or better at every stop, including a career-best mark of 57.9% at his current stop in High-A Modesto. Unlike many ground ball pitchers, however, the Spokane-native has also showed off the ability to fan batters at a significant rate, posting 11.9 K/9 through 27.1 career innings. Between his strikeouts and ground ball outs, Mills has been retiring nearly 85% of opposing hitters, minimizing the offensive threat any time he toes the rubber.

Upon his selection by the Mariners last June, the M’s had scouted Mills as typically throwing in the 91-92 range, but he’s reportedly touched as high as 96mph this season with Modesto. No small part of that uptick in velocity can be credited to his work done over the winter.

Mills worked in the offseason with Seth Heckel--a strength and conditioning coach at Heckel Strength Training who works specifically with a handful of collegiate and minor league baseball and softball players--where his primary goals were to stay healthy and build strength. His process began with a movement assessment that analyzes any asymmetries in his body in an effort to discover any muscles or joints that may be compensating when performing powerful, explosive movements, such as pitching a ball 90+ mph. This assessment allows Heckel to build a workout plan to strengthen any potentially problematic areas to ensure health over the grind of a full minor league season.

Mills’s trainer, Seth Heckel, gave us an overview of what the lanky pitcher worked on over the off-season:

“Our primary goal is to keep him healthy, so a lot of what we do is with the goal of accomplishing that. Our secondary goal is to build strength. Some unique things we do: we do A LOT of quarter squats, which are exactly like what they sound like. He gets into a quarter squat position and explodes up. When he first started (before he was drafted), he could quarter squat around 275lbs and before he left for Spring Training this year he was repping about 450lbs for sets of 8. Almost all athletic movements are performed from the quarter squat position. Pushing off the rubber is performed from the quarter squat position with the back leg, so we really wanted to work on being powerful from that position to increase his velocity. We also do a bunch of lumbopelvic control and balance drills because research done on minor league ballplayers has shown increasing lumbopelvic control directly led to an increase in pitching performance. In short, his lifting programs are specifically built to ensure he is moving well before those movements are loaded, and they are built with specific goals related to baseball and pitching.”

When asked about whether Mills’ unique delivery makes it more difficult for him to generate velocity, or if it perhaps increased his risk of injury, Heckel continued:

“There are also differing opinions on if it is more difficult to throw harder sidearm vs. over the top. Some say with a sidearm delivery, your arm is further away from your body, which makes it more difficult (like carrying something heavy away from your body versus close). Others will say it’s due to a difference in trunk rotator vs flexor muscles, and a lot more arguments get thrown around. In my opinion it is harder to throw hard sidearm, that’s why we don’t usually see a lot of velo from down there. For me, it just means we emphasise taking care of his Wyatt’s rotating core muscles because he is going to use the hell out of them (every baseball players does, but him probably even moreso).”

Heckel repeatedly praised Mills—who MLB.com’s Prospect Pipeline lists as the Mariners’ #10 prospect—for his dedication and hard work in the offseason, crediting his commitment to perfecting his craft as a major factor in his success.

Mills has only been in Modesto for a few weeks, but he’s already looking like he’s got Cal League hitters overmatched. Look at the nasty late movement on this fastball:

Note too that unlike some righty sidearmers whose cross-body motion causes them to fall off the mound, Mills lands in a power quarter squat position, ready to field comebackers or sprint to first base—especially important for a pitcher who generates a lot of weak contact and ground balls.

The 23-year-old has allowed just one baserunner over his last three appearances, and has shown an ability to work multiple innings, as he’s had outings of 1.2, 2.0, and 2.0 innings pitched already this season. While it’s uncommon for players to make the jump from any level of A ball directly to the majors, look for the polished college product to move quickly as the weather grows warmer, especially if his uptick in velocity hangs around. Mills possesses the perfect combination of talent, deception, and results that could continue to propel him through the system at a rapid rate, landing him in Seattle much sooner than many expect. Not bad for a guy whose scouting report on MLB’s live coverage on draft day was essentially a hasty on-air read of facts from his “Gonzahga” bio.