The hidden benefit of pulling the ball

Everything else about the opportunity being equal, corner OFs have a significantly harder time catching pulled balls  than they do catching opposite-field balls.  In this piece, I’ll demonstrate that the effect actually exists, try to quantify it in a useful way, and give a testable take on what I think is causing it.

Looking at all balls with a catch probability >0 and <0.99 (the Statcast cutoff for absolutely routine fly balls), corner OF out rates underperform catch probability by 0.028 on pulled balls relative to oppo balls.

(For the non-baseball readers, position 7 is left field, 8 is center field, 9 is right field, and a pulled ball is a right-handed batter hitting a ball to left field or a LHB hitting a ball to right field.  Oppo is “opposite field”, RHB hitting the ball to right field, etc.)

Stands Pos Catch Prob Out Rate Difference N
L 7 0.859 0.844 -0.015 14318
R 7 0.807 0.765 -0.042 11380
L 8 0.843 0.852 0.009 14099
R 8 0.846 0.859 0.013 19579
R 9 0.857 0.853 -0.004 19271
L 9 0.797 0.763 -0.033 8098

The joint standard deviation for each L-R difference, given those Ns, is about 0.005, so .028+/- 0.005, symmetric in both fields, is certainly interesting.  Rerunning the numbers on more competitive plays, 0.20<catch probability<0.80

Stands Pos Catch Prob Out Rate Difference N
L 7 0.559 0.525 -0.034 2584
R 7 0.536 0.407 -0.129 2383
L 9 0.533 0.418 -0.116 1743
R 9 0.553 0.549 -0.005 3525

Now we see a much more pronounced difference, .095 in LF and .111 in RF (+/- ~.014).  The difference is only about .01 on plays between .8 and .99, so whatever’s going on appears to be manifesting itself clearly on competitive plays while being much less relevant to easier plays.

Using competitive plays also allows a verification that is (mostly) independent of Statcast’s catch probability.  According to this Tango blog post, catch probability changes are roughly linear to time or distance changes in the sweet spot at a rate of 0.1s=10% out rate and 1 foot = 4% out rate.  By grouping roughly similar balls and using those conversions, we can see how robust this finding is.  Using 0.2<=CP=0.8, back=0, and binning by hang time in 0.5s increments, we can create buckets of almost identical opportunities.  For RF, it looks like

Stands Hang Time Bin Avg Hang Time Avg Distance N
L 2.5-3.0 2.881 30.788 126
R 2.5-3.0 2.857 29.925 242
L 3.0-3.5 3.268 41.167 417
R 3.0-3.5 3.256 40.765 519
L 3.5-4.0 3.741 55.234 441
R 3.5-4.0 3.741 55.246 500
L 4.0-4.5 4.248 69.408 491
R 4.0-4.5 4.237 68.819 380
L 4.5-5.0 4.727 81.487 377
R 4.5-5.0 4.714 81.741 204
L 5.0-5.5 5.216 93.649 206
R 5.0-5.5 5.209 93.830 108

If there’s truly a 10% gap, it should easily show up in these bins.

Hang Time to LF Raw Difference Corrected Difference Catch Prob Difference SD
2.5-3.0 0.099 0.104 -0.010 0.055
3.0-3.5 0.062 0.059 -0.003 0.033
3.5-4.0 0.107 0.100 0.013 0.032
4.0-4.5 0.121 0.128 0.026 0.033
4.5-5.0 0.131 0.100 0.033 0.042
5.0-5.5 0.080 0.057 0.023 0.059
Hang Time to RF Raw Difference Corrected Difference Catch Prob Difference SD
2.5-3.0 0.065 0.096 -0.063 0.057
3.0-3.5 0.123 0.130 -0.023 0.032
3.5-4.0 0.169 0.149 0.033 0.032
4.0-4.5 0.096 0.093 0.020 0.035
4.5-5.0 0.256 0.261 0.021 0.044
5.0-5.5 0.168 0.163 0.044 0.063

and it does.  Whatever is going on is clearly not just an artifact of the catch probability algorithm.  It’s a real difference in catching balls.  This also means that I’m safe using catch probability to compare performance and that I don’t have to do the whole bin-and-correct thing any more in this post.

Now we’re on to the hypothesis-testing portion of the post.  I’d used the back=0 filter to avoid potentially Simpson’s Paradoxing myself, so how does the finding hold up with back=1 & wall=0?

Stands Pos Catch Prob Out Rate Difference N
R 7 0.541 0.491 -0.051 265
L 7 0.570 0.631 0.061 333
R 9 0.564 0.634 0.071 481
L 9 0.546 0.505 -0.042 224

.11x L-R difference in both fields.  Nothing new there.

In theory, corner OFs could be particularly bad at playing hooks or particularly good at playing slices.  If that’s true, then the balls with more sideways movement should be quite different than the balls with less sideways movement.  I made an estimation of the sideways acceleration in flight based on hang time, launch spray angle, and landing position and split balls into high and low acceleration (slices have more sideways acceleration than hooks on average, so this is comparing high slice to low slice, high hook to low hook).

Batted Spin Stands Pos Catch Prob Out Rate Difference N
Lots of Slice L 7 0.552 0.507 -0.045 1387
Low Slice L 7 0.577 0.545 -0.032 617
Lots of Hook R 7 0.528 0.409 -0.119 1166
Low Hook R 7 0.553 0.402 -0.151 828
Lots of Slice R 9 0.540 0.548 0.007 1894
Low Slice R 9 0.580 0.539 -0.041 972
Lots of Hook L 9 0.526 0.425 -0.101 850
Low Hook L 9 0.546 0.389 -0.157 579

And there’s not much to see there.  Corner OF play low-acceleration balls worse, but on average those are balls towards the gap and somewhat longer runs, and the out rate difference is somewhat-to-mostly explained by corner OF’s lower speed getting exposed over a longer run.  Regardless, nothing even close to explaining away our handedness effect.

Perhaps pull and oppo balls come from different pitch mixes and there’s something about the balls hit off different pitches.

Pitch Type Stands Pos Catch Prob Out Rate Difference N
FF L 7 0.552 0.531 -0.021 904
FF R 7 0.536 0.428 -0.109 568
FF L 9 0.527 0.434 -0.092 472
FF R 9 0.556 0.552 -0.004 1273
FT/SI L 7 0.559 0.533 -0.026 548
FT/SI R 7 0.533 0.461 -0.072 319
FT/SI L 9 0.548 0.439 -0.108 230
FT/SI R 9 0.553 0.592 0.038 708
Other L 7 0.569 0.479 -0.090 697
Other R 7 0.541 0.379 -0.161 1107
Other L 9 0.534 0.385 -0.149 727
Other R 9 0.550 0.497 -0.054 896

The effect clearly persists, although there is a bit of Simpsoning showing up here.  Slices are relatively fastball-heavy and hooks are relatively Other-heavy, and corner OF catch FBs at a relatively higher rate.  That will be the subject of another post.  The average L-R difference among paired pitch types is still 0.089 though.

Vertical pitch location is completely boring, and horizontal pitch location is the subject for another post (corner OFs do best on outside pitches hit oppo and worst on inside pitches pulled), but the handedness effect clearly persists across all pitch location-fielder pairs.

So what is going on?  My theory is that this is a visibility issue.  The LF has a much better view of a LHB’s body and swing than he does of a RHB’s, and it’s consistent with all the data that looking into the open side gives about a 0.1 second advantage in reaction time compared to looking at the closed side.  A baseball swing takes around 0.15 seconds, so that seems roughly reasonable to me.  I don’t have the play-level data to test that myself, but it should show up as a batter handedness difference in corner OF reaction distance and around a 2.5 foot batter handedness difference in corner OF jump on competitive plays.

3 thoughts on “The hidden benefit of pulling the ball”

  1. Visibility is a good theory. In addition, could trajectory play a role? I believe pulled balls will tend to have more topspin, giving them a lower trajectory, while oppo balls are more likely to be elevated. Obviously, you are controlling for time elapsed until the ball lands. But could it be that opposite field balls spend slightly more time at a catchable distance above the ground? Or stated another way, that a higher proportion of pulled balls would be catchable without requiring the fielder to dive?

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    1. Topspin should make the ball accelerate towards the ground, so for a given amount of time in the air, it should spend less time below the waist. Something like http://ffden-2.phys.uaf.edu/webproj/211_fall_2014/Max_Hesser-Knoll/max_hesserknoll/Images/TennisShotCompare.png It looks like the effect is there for CFs as well (I could have sworn I’d looked at that, but maybe I matched the wrong pairs somehow). The effect is a lot smaller for balls that come down near the same angle as the CF (which don’t have that much sidespin either way), but it’s there again, robust to hang time, once the CFs have a significant lateral component to their movement. Maybe it’s just that slices/slice swings are easier to read in general.

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