Mariners LHP Justus Sheffield showing breakout potential for 2020

It happens almost every spring. Somebody comes to camp, blows everybody away, and all of a sudden becomes everybody’s “breakout player” selection. This year, that player is quickly becoming Mariners’ starter, Justus Sheffield.

Justus Sheffield had an interesting 2019 season. The Mariners prize in the James Paxton trade, Sheffield began the season in AAA Tacoma and things went rather poorly. In 55 innings, Sheffield produced a 6.87 ERA and a 1.82 WHIP, with just 48 strikeouts along the way.

Sheffield made a 1-game Mariners debut and was sent back to the minors right after, but the woes in the PCL didn’t go away. Then the Mariners made a decision that may have changed the outlook of Sheffield’s career: they demoted him to AA Arkansas. And there, he flourished.

Working with Pete Woodworth, Arkansas pitching coach, Sheffield’s fastball command and plan of attack seemingly improved overnight. He made 12 starts for Arkansas, same as he did in Tacoma, but this time covered 78-innings of 2.19 ERA baseball, striking out 85 hitters and producing a 1.03 WHIP.

Getting out of the extreme offensive haven of the PCL and away from the MLB ball helped Sheffield, but the question was, how much? Well in August, the Mariners recalled Sheffield to pitch in the final 6 weeks of the season and the results were promising. Sheffield made 7 starts for Seattle and in 36 innings, he managed to punch out 37 hitters, generate a +50% groundball rate, and post a decent 4.71 FIP. Nothing spectacular, but definitely warranting another long look in the rotation.

Sheffield came to camp looking to build on his late 2019 success. To say he has thus far would be an understatement. Sheffield has appeared in 3 Cactus League games covering 8 innings. In those 8 innings, Sheffield has produced 12 strikeouts and a 0.625 WHIP. More importantly, Sheffield has yet to issue an intentional pass.

But numbers mean very little in Spring Training, so what are we seeing to make us believe that improvements have been made? One thing that has carried over for Sheffield is his great slider. The pitch is his go-to offering and generates insane swing-and-miss rates. Sheffield is also starting to throw his changeup more, which he is throwing with conviction and with great fade.

But the biggest upgrade has come with the fastball. Sheffield is commanding the pitch much better than in the past. And now, he’s even tinkered with the grip, moving from a 4-seam to a 2-seam pitch in his last outing, a change he may stick with for a while. His catcher, Tom Murphy, is certainly seeing a difference from young Justus Sheffield this spring:

"“His four-seam had very low spin to begin with, so him switching to a two-seamer actually is going to benefit him in the long run, and you saw that today… It’s one of those things where you kind of want to feed the beast, right? If a four-seam necessarily isn’t at the upper echelon, then why keep pushing something that isn’t going to be a great pitch? When you can make it a two-seamer, now all of a sudden, that low spin rate plays to his advantage.”"

Sheffield’s ability to maintain a breakout player tag may come down to how well he can make the fastball work for him. But his 2020 is off to a great start and with a rotation spot locked down, Sheffield can continue to tinker this spring.

Perhaps Sheffield’s “breakout” isn’t earth-shattering. Maybe it comes in the form of 160 innings of 4.3 FIP ball with 150-175 strikeouts and a good groundball rate. But that is a damn good season for a 24-year-old. Heck, that’s a good season for a 30-year-old arm. Sheffield is off to a great start, but only time will tell if he can keep this momentum heading into the regular season.