Gerrit Cole’s not-so-secret weapon


Gerrit Cole had a great outing yesterday in the Pittsburgh Pirates home opener, striking out eight over six innings while giving up three hits.  After a somewhat-middling outing against the Reds, it was a welcome sign for Pirates fans.  If you haven’t been watching Cole closely, you might make the assumption that Cole’s fastball was in play.  And it was.  So too was his not-so-secret weapon: his slider.

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About a month ago I detailed all of the best pitches of the Pirates’ starting rotation, using such advanced metrics as O-Swing %, O-Contact %, SwStr %, and ground ball/fly ball rates.  To refresh:  ‘O-swing %’ is the percentage of times an opposing batter swung at a pitch that is outside the strike zone.  This is an excellent metric to determine several tools at a pitcher’s disposal, including deception and movement.  ‘O-Contact %’ is the amount of times where those batters swung at a pitch outside the zone and also made contact.  ‘SwStr%’ is shorthand for swinging strike percentage, the percentage of time that an opposing batter swings at a pitch and misses.  This gives us an excellent indicator of a pitcher’s “swing and miss stuff.”

Second, I wanted to look at Cole’s batted ball movement.  The Pirates as a team have employed analytics into their game at such a deep level that they use shifts and batter tendencies to induce the highest ground ball-to-fly ball ratio in the majors, and as such, it is important for their pitchers to have ‘stuff’ that is complementary to that approach.

All in all, these items above serve my main criteria in determining a pitcher’s ‘best pitch.’  Here are the league averages for all of these stats:

2014 National League Averages
O-Swing %30%
O-Contact %66%
Ground Ball %44%
Line Drive %21%

Back then, I declared that Cole’s slider was his best pitch.  Since the time of that writing, I’ve made a mental note to check in on how the pitch would play for Cole in 2015.  After his excellent start yesterday, the time seems right to see how the slider is doing.  Here’s what I’ve seen so far:

Plate Discipline
(2014 statistics included for comparison)


In 22 starts in 2014, Gerrit Cole threw 286 sliders, or 13 per start if you prefer.  We can see that he had excellent numbers across the board in plate discipline., getting far more batters to chase outside of the zone than the league average.  When you add those together it’s not surprise that the swinging strike percentage on Cole’s slider was almost double the league average.

Gerrit Cole is a pitcher that is learning how to pitch in the majors before our very eyes.  The fastball got him to the big leagues.  The slider may end up deciding how long he stays.

In 2015, Cole may be leaning on the slider a bit more, with 16 per start.  The numbers have actually improved in the very early going, with the o-swing jumping up a full five percent while the contact rate is going down, leading us to a staggering 28.10% swinging strike rate.  I know that right now those reading this are saying “small sample size,” and while that’s true to an extent, when we look at Cole’s slider as the evolution of his go-to ‘strikeout’ or ‘get out’ pitch, sample size becomes somewhat irrelevant.  If the slider is truly becoming Cole’s marquee pitch as i suspect, the amount of times he throws it takes a backseat to how effective it is.

Let’s see what happens when hitters actually put Cole’s slider in play.

Batted ball metrics
(2014 statistics included for comparison)


When the slider is hit in fair territory, we see a bit of a different value, as it ends up being either a line drive or a ground ball, which is quite peculiar.  This is where small sample size can have a greater influence.  I fully expect these numbers to level out as the weeks go by, but for now we can reasonably assume that batters aren’t making good enough contact to drive the ball in the air, which will lead to small HR-FB% rates.

Gerrit Cole is a pitcher that is learning how to pitch in the majors before our very eyes.  The fastball got him to the big leagues.  The slider may end up deciding how long he stays.

Throwing all hyperbole out of the window, these numbers are flat-out exciting.  With the great strides that Cole’s secondary pitches took in 2014, expect to see the slider often this season.

Next: The best pitches of the Pirates' starting rotation