Seattle Mariners: 3 Breakout Candidates for 2020 Season

3. Justus Sheffield

We saw quite a bit of Sheffield in August and September this year and the results were a bit mixed. On the one hand, we saw a devastating slider and 92-96 MPH fastball from the left side. On the other hand, we never quite saw the third pitch take off and his command was a bit spotty.

But I like Sheffield for a relatively big breakout in 2020. What makes me so confident? 2 stats in particular: K/9 and groundball percentage. In his limited 36 innings with the Mariners in 2019, Sheffield posted a 9.25 K/9 and a 52.3% ground ball rate.

Those numbers by themselves are good. But when you compare them to other starters, you start to see exactly what Sheffield may be becoming. If he had enough innings to qualify, Sheffield’s groundball rate would have ranked him 6th in all of baseball amongst starters.

In groundball rate, he finished just ahead of guys like Stephen Strasburg, Sonny Gray, and Hyun-Jin Ryu. But by itself, who really cares? Brad Keller produces a lot of groundballs and he’s not great. And while that is true, I would point out that Keller was still a productive pitcher in 2019, posting a 2.2 fWAR.

But what makes me the most excited about Sheffield in 2020 is the groundball percentage combined with the punchouts. Amongst qualified starters, the number of pitchers with higher groundball% and K/9 numbers is a short one. Just Max Fried and Luis Castillo beat him in both categories amongst qualified starters. That is the whole list.

In raw K/9, Sheffield would have tied for 23rd with Noah Syndergaard. Now I know that a lot of this based on ridiculously small sample size. I get it. My argument is full of holes. But in that short time, Sheffield missed bats and got a lot of groundballs and those are facts.

The slider is a legitimate putaway offering, causing a whiff rate of 47.5% in 2019. The fastball has above-average velocity for a lefty and we saw a glimpse of a useable changeup and quite possibly a developing cutter in Septemeber.

I’m not saying that Sheffield is a Cy Young Award level pitcher. He still has command issues he needs to sort out and a third pitch to develop. However, Sheffield is a young, athletic pitcher who got his first taste of big-league action as a 23-year-old. Call me crazy, but a Robbie Ray type of season isn’t out of the question in 2020.

If I was betting on a breakout in 2020, I’d put the most money of Justus Sheffield. Perhaps it is just wishful thinking, wanting to believe that 37 innings is enough for me to tell. But my eye tells me the stuff, arm, and athleticism is there. If it all clicks for Sheffield, you wouldn’t want to be in the box against him in 2020.