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.