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How Do Arm Slots and Individual Pitches Effect Pitcher Splits?

It is no mystery that both real major league pitchers and OOTP pitches can perform better against one handedness or the other. Traditionally, most pitches perform better against their own handedness - lefty on lefty or righty on righty. OOTP models this, but what are these splits the result of? Is it randomness? Is there something under the hood that determine a pitcher's splits? Or is is determined by arm slot and/or pitch mix? If OOTP looks to realism, we know that both arm slot and the pitch repertoire should contribute to one's splits. Pitches like cutters and changeups are crucial in getting hitters of the opposite handedness out in the major leagues.

Using the OOTP 22 player editor, I could manually adjust arm slot and pitches a given player threw (along with how good that pitch was/would be - current/potential ratings). On the bottom of the page, a "resulting R/L platoon split" was adjusted as you changed different factors. If a ratio of 1.000 was observed, no splits were seen between same and opposite handedness. A ratio above one indicated splits in favor of same handedness. So a righty with an overall ratio above one would have splits that were better against righty hitters. A ratio below one indicated splits in favor of the opposite handedness. In this instance, a righty's splits would show the pitcher has splits that were better against lefties. The further below or above one that was observed, the worse splits the pitcher had.

The first factor that was looked at was arm slot. It's intuitive that the more over the top a pitcher threw, the less splits that would be observed. This was in fact the case. After calculating each max pitch splits value (250 for both current and potential rating), they were averaged together to see the effect of arm slot on the splits ratio. The averages were 1.01 for over the top, 1.05 for normal (3/4), 1.17 for sidearm and 1.27 for submarine. So overall, over the top and normal arm slots give us less splits from a pitcher, while sidearm and submarine give us more splits.

Next, I wanted to take a look at how individual pitches effected a pitcher's splits ratio. I found that each individual pitch does, in fact, have an impact of the splits ratio. If more than one pitch is in a player's repertoire, those pitches are weighted on how good the pitch is and then averaged. If a player throws 3 pitches that are all 55 in current rating, the pitch split ratio is just the average of the 3. If one pitch is an 80 in current rating and the other two are 55, the 80 pitch will carry more weight in the average to determine the splits ratio. In order to look at the effect of each pitch on the splits ratio, I cleared each pitch in the pitcher's repertoire (set to 0 out of 0) and maxed out each pitch (250/250) individually and recorded the splits ratio. I did this for each of the 4 different arm slots. The results can be seen here:

So why is this important if you can see the splits of a pitcher? Well, by knowing a pitching prospect's arm slot and repertoire, you can get a good idea at what type of splits the player will grow into. If you have a shutdown RP prospect that will throw a great slider and sinker (see Eric Dahlke), you can expect very large splits favoring the same side handedness. However, if you see a pitching prospect with an average slider, but has a good changeup and curveball then the splits won't be as bad. You can even project if a guy will have reverse splits. Take Ben Golar for instance. Firstly, he throws over the top, which we know diminishes the splits as much as possible. Secondly, his repertoire consists of three pitches: fastball, cutter and changeup, all of equal weight. We know that for an over the top pitcher, the fastball is slightly favoring of the same side handedness, while the cutter and changeup favor opposite side handedness. So how did his actual rankings shake out? 50/60/45 against righties and 55/60/45 against lefties. Reverse splits that I could have predicted from the day I drafted him.

The last study I wanted to conduct was how a pitch that develops over time would effect the splits ratio? In other words, would a 40/70 (current/potential) changeup reduce the splits as it developed. The short answer is that it does. The pitches current rating is what factors in to the splits ratio and since each pitch is weighted, as it gains more weight, it impacts the splits ratio more heavily. To test this, I created an normal (3/4) arm slot arsenal of 3 pitches: Slider, Splitter and Knuckleball, all of which were maxed in both current and potential ratings (250/250). I also gave this pitcher a changeup but with a zero current rating and a maxed (250) potential rating. The splits ratio for this setup was 1.1 (favoring the same handedness). I measured the change in the splits ratio as I slowly increased the current rating of the changeup:

From the graph you can see that as the changeup developed, the splits ratio pulled closer to 1. This makes sense, as the changeup is a pitch that favors the opposite handedness. So if you are looking at a prospect with bad splits, you can see an improvement on those splits if there is more development in pitches that would bring the splits towards 1.

Hopefully this serves as some useful information and you all have a better understanding of how arm slots and pitches can influence splits. Splits certainly aren't the end of the world, but they do matter and being able to appropriately project a pitcher's profile can give you a leg up.

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