Jordan Zimmermann, Now With Strikeouts

Despite possessing above average fastball velocity, Jordan Zimmermann has generally posted strikeout rates right around the league average. Part of the reason for the disappointing strikeout totals is because he throws his fastball quite frequently. From 2011 to 2013, his fastball usage ranked 29th among 125 qualified starters. We know that the fastball easily sports the lowest SwStk% among all pitch types. So throwing the pitch often is naturally going to result in fewer swings and misses on average.

Prior to 2013, Zimmermann’s secondary pitches weren’t very good at generating swings and misses. Both his slider and curve induced swinging strikes at a below average clip. The former failed to make up for the lack of whiffs by inducing grounders, while the curve ultimately proved to be a decent pitch because it offset its lack of whiffs with its ability to generate lots of grounders.

Then in 2013, the results on his slider improved dramatically, as it was suddenly generating an above average rate of swinging strikes. That improvement continued into 2014, as the pitch’s SwStk% jumped again. But the real driver of Zimmermann’s strikeout rate surge was his fastball. The pitch’s SwStk% remained in a tight range between 6.2% and 6.4% from 2011 to 2013, but rose to 8.4% in 2014. He also upped his usage of the pitch to over 70%, ranking fourth among all qualified starters.

You usually don’t see increased fastball usage coinciding with a spike in strikeout rate. The velocity on the pitch remained identical to his mark since 2012, so it’s curious how he was suddenly able to induce so many more swings and misses with the pitch. The smart money says to expect some regression here without any obvious explanation for why the pitch was so much more effective.

The risk is that if the fastball returns to its previous SwStk% level, but he decides to continue throwing it 70% of the time, his strikeout rate may actually drop below his 2011-2013 levels. Though, a better slider could curb some of that downside.

Of course, even if his strikeout rate does drop back, his control is so good that he’s going to remain a good pitcher. His overall strike percentage ranked third in baseball this season and fifth last year. And since 2012, he ranks third in F-Strike%. That type of strike-throwing ability should help him maintain a sub-5% walk rate.

Aside from questions surrounding the sustainability of his increased strikeout rate, one wonders how much longer he can continue to outperform his SIERA marks. Except for this year, he has always posted below average BABIP marks, despite allowing high line drive rates since 2012. And in two out of his four full seasons he has posted HR/FB rates below 6.5%. His home park does suppress home runs, but not to such an extreme degree. Without any real explanation for how he is accomplishing his prevention of both hits on balls in play and homers on fly balls, we cannot be sure how long those apparent skills will last.

Zimmermann seems to be a safe bet, but he’s precisely the type of pitcher that will rarely, if ever, appear on my fantasy teams. His strikeout rate surge looks to be a bit of a mirage and I would rather bet on a pitcher maintaining a strong skill set than a low BABIP and HR/FB rate.