Clayton Kershaw's Slider Is Sick-Nasty

[Edit 2: Since the original post, I found that some of the later plots had incorrect parameters, and therefore, should be ignored. They do not accurately represent Kershaw's swinging strike and contact percentages. You can take a look at the updated swinging strike percentages for his slider and curveball here.]

Sir Clayton Kershaw, he of the curveball nicknamed by Vin Scully "Public Enemy No.1," has been mighty magnificent this season with a 3.03 ERA and 163 K's through 157.1 innings (a side note: I would have linked the Youtube clip of Scully's call of Kershaw's huge curveball striking out a stunned Sean Casey during March 2008, but it was gone a week or so after I saw it over two years ago).

[Edit: Here's a grainy video of Scully's call at metatube, hat-tip to Bill Plaschke's sweater.]

But I believe that it's really been Kershaw's slider that has been helping him so much as an additional new toy for him to fool batters with. It's always great to add another pitch to a tandem arsenal like Kershaw's fastball/curveball combination, and the effectiveness of Kershaw's slider really shows how Kershaw has another weapon to induce swinging strikes. According to Fangraphs, Kershaw threw his slider on 7% of pitches in 2009 but 19% of pitches in 2010 so far.

Let's conduct a closer examination of Kershaw's pitch types since his ML debut by looking at the month-by-month table below to show when Kershaw introduced his slider and how much he's used it since then:



Keen Dodger fans have taken note of Kershaw's use of his new slider, but I didn't know he started using it so much, or significantly more than his famous curveball. If you check this out, you'll notice that he introduced his slider sometime during June 2009. Since then, he's gradually used his slider more and more and his curve ball less and less. This doesn't mean that his slider is more effective than his curve ball, as part of a pitcher's effectiveness is his ability to mix and match and locate different types of pitches given the previous pitch (for what it's worth, Kershaw's pitch type values at Fangraphs show that his above-average slider has been more valuable than his below-average curveball this season, attaining a 1.63 wFB/C and a -0.82 wCB/C, but please ignore those numbers if you don't know what they stand for).

Let's take a quick look at the pitch movement plots of Kershaw's curveball and slider:

Looks like Kershaw gets a lot of movement on both his curveball and slider, but it's the vertical movement of his curveball that sticks out here. That 12-6 break that everyone always talks about has really made his curveball into a filthy moving pitch. The slider isn't too shabby either, with huge horizontal movement to the left (from the catcher's perspective).

This brings up some interesting questions I have about Kershaw. Suppose I want to take a look at the effectiveness of Kershaw's curveball vs. Kershaw's slider (and yes, I do). For a few weeks now, I've been playing with my PITCHf/x database and learning to make pitch location plots, including the hexagonal binning plots you see above. However, it's difficult to compare between two types of pitches for the same criterion, say, swinging strikes on Kershaw's curveball vs. swinging strikes on Kershaw's slider, especially for normal scatter plots, because all you see are a bunch of dots (see my recent post about Jonathan Broxton and you'll know what I'm talking about). You can get information about where Kershaw locates his two pitches to induce swinging strikes, but you can't compare how well Kershaw does it with his curveball vs. his slider just by simple scatter plots. I suppose I could just show a table of Kershaw's swinging strike percentage by pitch and by month, but it's more telling and effective (and fun) to see the pitches in the strikezone for yourself.

Enter Dave Allen and Jeremy Greenhouse. I believe the idea of plotting PITCHf/x data in the form of heat maps was first popularized by Allen, and Greenhouse has also done fantastic work with heat maps of his own. With the help of both of these guys, I was able to figure out how to fit a surface model and plot them on filled contour plots. In this case, instead of plotting the actual curveballs that Kershaw pitched that caused a swinging strike, I ran a model to predict swinging strike percentage based on location, looking at all of Kershaw's curveballs and how often those pitches caused a batter to swing and miss. Creating a filled contour plot, much like what you see in infrared imaging and topographical elevation mapping, allows me to smooth out the data in order to see if there are any trends.

It's fitting that I make my first of these images for the Dodgers' best (read: best) starting pitcher, Clayton Kershaw. Let's take a look at the first of them, shall we? Here's Kershaw's swinging percentages on curveballs:



Note that there were 901 curveballs against RHH and 235 curveballs against LHH. I scaled the colors on the graph to range from 0% to 60% (shown as 0.0 to 0.6 in the legend) so that you can compare these with the slider graphs later, red being a very high swinging strike percentage, blue being near zero swinging strike percentage. I suppose the scale would be better read if I put them in percentages, but I'll discuss these values in 0-100% terminology rather than 0.0-1.0.

Let's discuss Kershaw's curveball. First of all, recall that Kershaw has great negative vertical movement as well as negative (left in the catcher's view) horizontal movement. As a left-handed pitcher, curveballs will go down and toward right-handed hitters and down and away from left-handed hitters. If you take a look at the bottom lefthand corner for left-handed hitters, you'll notice a green "hill," showing that Kershaw gets up to 30% of LH batters to swing and miss out of the zone when he throws his curveball there. The middle of the zone and low outside the zone actually get left-handed hitters to swing and miss the most. And as expected, LHH whiff more often overall than RHH on Kershaw's curveball.

However, the most interesting part is where you see a shade of green in the middle of the strike zone for right-handed hitters, where about 45-50% of RH batters whiff. But there's a blue spot to the immediate left of Kershaw's "hot spot," which looks like the spot where right-handed hitters get the sweet spot of the bat (or at least, contact). With a curveball as huge of a vertical break as Kershaw has, sometimes there's not much a hitter can do when he sees it coming toward the strikezone but to swing and hope it connects with the ball. In this case, that blue spot might just be where the batter swings and connects most often (and where Kershaw should avoid with his curveball).

Let's compare this with the swinging strike percentage of Kershaw's newest pitch, his slider, again looking at handedness splits:



Note that there were 473 sliders against RHH and 188 sliders against LHH. There's a lot more color in this plot, which tells us right away that Kershaw's sliders are getting more batters to swing and miss than his curveballs. The entire outside edge for lefties has up to 60% swinging strike percentage when batters are fooled and swing and miss, while the middle of the strikezone causes even more whiffs for righties. Low sliders also look like they fool both RHH and LHH.

Remember that these are models, not the actual pitches themselves, and that in order to get this graph to look smooth, the model may have overemphasized some hot spots. This is due to sample size. Still, it's very clear from these graphs that hitters swing and miss on a higher percentage of Kershaw's sliders than his curveballs.

Swinging and missing a lot means less contact. Let's take a look at hitters' contact percentage on Kershaw's curveballs and sliders, seeing if they agree with the previous swinging strike percentage plots:



Some good stuff here. Not sure what to make of the long red streak down the middle of the RHH graph, but perhaps that's where right-handed hitters make contact (fouling off pitches possibly?). Right-handed hitters make contact throughout much of the strikezone, around 30% to 45%, while left-handed hitters make contact mainly in the middle and/or up in the zone or out of it. I believe the red spot (50-60%) out of the zone is where many left-handed hitters foul off hanging curveballs. Either way, hanging curveballs that are up in the zone, even out of the zone, do not bode well for Kershaw, as they cause both righties and lefties to make decent contact.

Let's compare this with the contact percentage of Kershaw's slider, again with handedness splits:



At first glance, it looks like that hitters get more contact off Kershaw's sliders due to the red. But notice that most of the red for both RHH and LHH is out of the zone, likely meaning that although hitters make contact 60% of the time or more, they are probably mostly foul balls or pop-ups. Still, it's a vulnerable spot to leave a hanging slider. But notice that there is very little contact in most of the strikezone (the lucky ones who do get hits off Kershaw's best-placed sliders are drowned out by the many many more unlucky ones who don't). At the very least, Kershaw's sliders do not draw as much contact, and presumably hard contact from hitters as compared to his curveballs.

Remember how I mentioned earlier that Kershaw's curveball this season has been more valuable than his slider, according to Fangraph's run values? All of the plots seem to agree that Clayton Kershaw's newest pitch is even more effective than the one he is most known for. Not only does Kershaw's slider cause more batters to whiff than his curveball, but hitters are less likely to make contact off his slider as well. Maybe there is a new Public Enemy No.1 that less people are talking about. I prefer to call it Kershaw's sick-nasty slider.