Deleting the Adjectives: Explaining Zimmermann

Before we begin let me apologize for not being able to write last week, as some of you may know I am still a student and with that comes exams, so my attention was elsewhere. Alright let's get on with the show.

Jordan Zimmermann has elevated his game this year. This is probably the truest true fact about the 2013 Washington Nationals. He currently possesses a 1.69 ERA and .87 WHIP, while going 7-1 in eight starts. He is going deeper into games too, pitching seven or more innings six times already, two-thirds of his 2012 season total of nine. This is known. What we want to know though, is why has he been so good?

The first immediate answer that jumps out is that opponents have a .230 batting average on balls in play or BABIP. This is significantly lower than his BABIP in 2011 and 2012, which were .291 and .288 respectively. While the often refrain with BABIP is that it will eventually normalize to somewhere in the range of .290 to .320, this isn't a hard and fast rule. In any case, runners are finding it harder to get on-base when they put the ball in play against Zimmermann.

Peeking behind that, we can find a possible explanation for the depressed BABIP. According to Fangraphs batted ball data, Zimmermann's ground ball to fly ball ratio has risen from 1.30 in 2012 to 1.73 in 2013. So he's making hitters put the ball on the ground more often, which should lead to more outs, as the ball stays in the infield. In line with that, Zimmermann currently has the highest ground ball rate of his career at 49.4%, up from 43.4% in 2012 and 39.4% in 2011.

But that's not all. When Zimmermann does give up a fly ball, he's limiting its damage. His home run to fly ball ratio has fallen from an average 9.2% to an excellent 4.1%. Along with that, currently 16.3% of fly balls he does allow are in the infield. So Zimmermann is making sure that when hitters do put the ball in play, it's in the way he wants them to.

Possibly related to the control Zimmermann is holding over opposing hitters, he is stranding 83.3% of base runners, the best rate of his career. That 83% is also the best rate on the Nationals and is good for fourth in the National League. So Zimmermann has been excelling at keeping opposing hitters off the bases and when they do manage to get on base, they don't go anywhere.

But what has Zimmermann changed to exert so much control over opposing hitters? Well both the PITCHf/x and Baseball Info Solutions pitch tracking data show that he is throwing his fastball about 5% more often than he has the last few seasons, with his slider usage lowering by about the same amount. Zimmermann is attacking hitters with his fastball and not getting into deep counts, throwing on average just 3.45 pitches per plate appearance.

So Zimmermann is going after hitters and exerting complete control over the result of at-bats. That control is resulting in the consensus Cy Young winner stats seen at the beginning of this post. While what this is not predictive of future results, it is a good explanation for how he has been so dominant so far this season. If he can keep it up, Zimmermann may very well find himself possessing a Cy Young award at the end of the season.

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