Visualizing the Platoon

The Platoon Split
The "Platoon" split is one of the most interesting statistics in baseball. Simply put, it is the statistical split that documents the usual advantage a pitcher gains while pitching against hitters that hit from the same side as he throws.

The Platoon split has been discussed heavily is Sabermetrics; a section in The Book deals with its analysis and documentation, and an article by Dan Fox at Baseball Prospectus reveals the following:

"Platoon advantages exist and are significant, and that the difference is larger for left-handed hitters than for right-handers...The average left-handed hitter hit 34 points better against right-handers, but that the difference from the mean spans a range from 12 to 45 points (34 plus and minus the standard deviation of 22 points). For right-handed hitters the mean value for batting average is 18 points with an average spread of between 1 and 35 points. As you can see, there is a fairly large amount of variability for hitters from both sides."

But what causes the platoon split? Color commentators often describe hitters as being "uncomfortable" against pitchers with substantial platoon splits - because they "hide the ball well" or have "deceptive deliveries". I think focusing on the pitcher is important, but not nearly as important as focusing on the pitch.



A Matter of Perspective
Suppose we were to break down hitting into two parts: part perceptual and part motor. The perceptual part deals with the visual recognition of the pitch, and is thus affected by things such as the similarity of the various pitches thrown, the ability to quickly guess at the final location of a pitch on a particular trajectory, and the ability to judge the speed of the pitch. The motor part deals with the physical actions required to hit the ball, such as the action of swinging the bat, adjusting to the ball mid-swing, etc.

Presumably, the advantage for a Left Handed Hitter (LHH) against a Right Handed Pitcher (RHP) - or vice versa - is not a motor one. LHH do not get any advantages in terms of the amount of time it takes for the ball to reach the plate, nor would we say that they get any extra boost in power or quickness as a result of being on the opposite side of the pitcher. If anything, the ball is hidden from their view for a longer amount of time while most pitchers complete their delivery. How is that that LHH are better against RHP, and RHH are better against LHP?

Hitting a baseball starts with a complex visual discrimination task that literally takes place in the blink of an eye. Before he has time to think, the hitter must react to the pitch at hand - and do so with very little information about the pitch. The hitter sees only part of the trajectory of the ball clearly before "deciding" to swing.

Most of the time, when you see the trajectory of the ball, you view it from a very different angle than the hitter. Usually you see an offset pitcher's perspective of the pitch, over one of his shoulders; sometimes you get the "behind the plate" view that shows you essentially the Umpire's perspective. In recent years, some ballparks (especially Fenway Park) have adopted a much better viewpoint, from directly behind and over the head of the pitcher, which gives us a much clearer view of how pitches move as they approach the plate. But as viewers, we're fundamentally crippled by the fact we never get to see pitches as hitters do, which makes it very difficult to understand why pitches are so deceptive.

Enter PitchFX, which allows us to precisely capture the trajectory of each pitch. The PitchFX system accurately represents the pitch at every point along it's violent flight to the plate, and so, if we wanted, we should be able to do some tricky math to figure out what the trajectory looks like from various points on the field. This technique was first examined by Mike Fast, who, in addition to doing many other very clever things with PitchFX data, alerted us to the idea that views from the LHH batter's box might be different than from the RHH box, and also published a technique for applying the transformation. Specifically, concerning one pitcher-hitter matchup, he says, "The fastballs look almost straight to the right-handed hitter, and the breaking pitches have a noticeable hump; however, all the pitches appear to bend more sharply to the left-handed hitter, and the trajectories overlap more. If all left-handed pitchers' repertoires look somewhat like this, no wonder left-handed batters have a harder time with them than right-handed batters. It makes me eager to apply this technique to other pitchers."

The Data
So, now that we know how we got here, let's take a look at what we're dealing with. As a sample case, we're going to use Justin Masterson, an RHP for the Red Sox with a sizeable Platoon split and a strong sidearm delivery that primarily throws three pitches: a 2seam fastball, a 4seam fastball, and a slider (we will not deal with the occasional Masterson changeup since I will not graph plots with any thrown).

People like me always get accused of not actually showing the real behavior before we delve into the statistics, so let's take a look at Masterson on the mound, delivering a pitch. His sidearm release is very clearly shown.



If we abstract that back into data recorded by the PitchFX system, you will see that we get a relatively faithful and consistent representation of his release point.



So, Masterson is a heavy side-armer. PitchFX can see that. Things are working so far. Let's next take a look at one of the most traditional PitchFX graphs, which shows the Horizontal and Vertical movement on his Pitches. The Horizontal Axis here is horizontal movement from the Catcher's Perspective, due to the amount of spin that Masterson puts on the ball. In other words, this shows the amount of action that Masterson has put on the pitch. The same is true for the Vertical axis, which shows that most of Masterson's pitches have relatively low vertical movement (compared to other fastballs, this is why he is termed a "sinkerballer"). In this graph, we can easily identify three groups of dots: the cluster on the right is his slider, the cluster on the left can be split into his sinker and 4seam fastballs.




This gives us an idea of the kind of movement that Masterson is putting on his pitches: lots of horizontal movement with a very large difference between his sinker (which cuts in very heavily to RHH) and his slider (which cuts away very heavily), both of the pitches thrown with relative sink. We should also note the relative similarity in speed in these two pitches: the 2seamer (sinker) is thrown at about 90mph, the slider at about 84mph.

Many PitchFX breakdowns would stop here - we've documented the slider and the sinker, and how each break. But this PitchFX breakdown is intended to explain why Righties have so much harder a time against these two pitches than Lefties. Let's take a look at another view, which attempts to plot the trajectories of the pitches as they're seen from the Umpire's perspective. This plot shows every pitch thrown in this appearance, with the trajectories colored to represent faster (more red) and slower (more blue) pitches.




Okay, so we see how disturbing those trajectories appear from his release point. I think from this angle we can get a good idea of just how much movement is on each of these pitches, but it's even better from up above, looking down on the pitch:




We can also average those trajectories, to try to get an even better view of what's happening when he throws the ball:



Now the two very different horizontal trajectories of the slider and two-seamer are incredibly apparent. One pitch breaks very heavily inside to RHH, and one breaks outside to RHH. But does this really explain the Platoon?

I would argue - no, not quite. The Platoon split isn't really about stuff, in the sense that LHH have essentially the same dilemma to face with Masterson, they have one pitch that breaks strongly away and one that breaks strongly inside. So what is it about Masterson that's so disturbing to RHH?

For this we turn to Mike Fast's Batter's Box plots, which can show us that hidden hitter's perception, as the pitch is viewed from the Batter's Box. Let's take the LHH case first, remembering that they do relatively well against Masterson:



The big, sweeping slider is easily identified among the 2-seam fastball, as we can clearly see the large humps in the trajectory that identify it as the slider. In other words, the perceptual problem for LHH is pretty easy, because the slider and the 2seam fastball have such different trajectories when viewed from the LH side of the plate.

But then, what does a RHH see when they see Masterson's stuff? What creates the Platoon split?



The slider is gone! Well... not gone, but not visible, either. Of the eleven pitches on that plot, FIVE are sliders. Try and pick them out based on just the trajectory information: it's a mess. For RHH, the sinker/slider combo is pure deception, because there's no more simple heuristic to identify the pitch. This, and not discomfort, delivery, or magic, looks to be the source of the platoon split. When viewed from the batter's box, these two pitches appear wildly different. To LHH, they are easily identifiable and non-remarkable; to RHH, they are nearly indistinguishable.

Final Thoughts
Are there other things that contribute to the Platoon split? Absolutely. Stuff matters - the extra 7mph on the inside part of the plate, combined with the heavy sinking motion of the 2seamer, absolutely creates problems for RHH when they come up against a guy like Masterson. But this visualization shows us that sometimes, these well documented, traditional splits in baseball, that influence everything from relief pitcher usage, pinch hitter usage, and the advent of the LOOGY, might really be due to a simple difference in perception.


Note for Readers
All of the above plots can be generated using my freely available PitchFX tool. To generate viewpoint plots, select "Pitch Types" as the plot type and they will automatically appear.

Thanks
Thanks to the countless articles by Mike Fast, Josh Kalk, John Walsh, Alan Nathan, and many others, for making PitchFX so accessible and fun.

Link to this Post - 7/27/2008 01:47:00 AM -

4 Comments:

Blogger Dave said...

Dan, did you read John Walsh's article about the source of platoon splits in last year's THT Annual?

July 28, 2008 8:47 PM  
Blogger ieshan said...

Sadly, no, no access to it. If you have a copy or a synopsis I'd love to see it.


A couple people have mentioned it, but no one has said: What were the conclusions?

July 28, 2008 8:59 PM  
Blogger Dan Brooks said...

Er, above comment was mine. For some reason it didn't turn my email address into my name.

July 28, 2008 9:00 PM  
Blogger Mike Fast said...

John's conclusions:
"What I've found in this study is that, perhaps contrary to conventional wisdom, it is primarily the fastball and slider that contribute to large platoon splits, while the curveball and changeup are much more platoon-neutral."

He goes on to speculate, "You can imagine the true reason for the platoon split is simply the fact that the batter gets a 'better look' at an opposite-handed delivery. This makes sense, actually, because the opposite-side batter gets a bit more of a 'side view' of the pitch, which likely helps the perception of where the pitch is headed and its speed."

He also said, "Additionally, a study of sidearmers, or more generally, the variation of platoon split with arm angle, would certainly shed additional light on the subject."

Hopefully that's a fair summary without copying too much of the article.

July 30, 2008 10:18 PM  

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