A closer look at Gerrit Cole's platoon splits

Gerrit Cole's unbalanced platoon split this season is well-documented. Cole's struggles against left-handed hitters are a dramatic departure from the .223 batting average and .597 OPS he allowed vs. LHBs in 2015.

Batter	BA	OPS	OPS+
LHB	.316	.802	116 (career high)
RHB	.229	.584	62

The difference in platoon splits largely accounts for the drop-off from his elite performance last year. In 2015, he allowed only 7.9 h/9 and posted a 1.091 WHIP. This year he is allowing  more hits than innings pitched and has the highest WHIP of his career.

Ball-strike counts is another, less widely discussed split, which also shows a substantial change from 2015. Cole is pitching much worse than league average when ahead in the count.

Count	2015 OPS+	2016 OPS +
Batter ahead	85	67
Even	67	93
Pitcher ahead	70	121

Digging deeper, Cole's has a 128 OPS+ in two strike counts, which is a 76 point increase from last season. Here's a closer look at the difference in two strike counts from a year ago:

Year	2-strike OBP	Rank among SP with 15 GS	2-strike WHIP	Rank among SP with 15 GS
2015	.199 (.228 vs LHB)	18th out of 150	0.699	15th out of 150
2016	.301 (.336 vs LHB)	120th out of 128	1.230	120th out of 128

The interesting thing about these two splits is that they are related. Cole's platoon splits are almost wholly accounted for by his pitch count splits. More specifically, virtually all of the increased success of left-handed hitters against Cole is coming in two-strike counts. Another table:

Year	LHB / RHB, Batting average 2-strikes	LHB / RHB, Batting Average less than 2 strikes
2015	.169 / .192	.361 / .297
2016	.274 / .210	.367 / .248

Left-handed hitters are hitting over 100 points higher against Cole with two strikes this season. Indeed, if Cole was duplicating his 2015 success against LHB in two-strike counts, his batting average allowed vs. lefties overall would drop to .260, which is only two points higher than last season.

But it's not just two-strike counts against LHBs, in general, that are causing the problem. Zeroing in even further, we see that two-strike fastballs are at the root of the platoon split.

Cole has faced left-handed batters in two-strike counts 119 times this season. Of those, 61 have been resolved after he threw a fastball. Of those, 20 have resulted in hits (.328 batting average). Last season, only 12 of 120 plate appearances with two-strikes vs. LHB resulted in hits after he threw a fastball (.100 batting average). If Cole was seeing the same success with his fastball vs. lefties in two-strike counts this season, his total platoon split vs. LHB would drop to a .245 batting average (remember he allowed a .258 BA vs. lefties last year).

Now, obviously, one can't draw such easy hypotheticals. If he was getting more left-handed batters out with his fastball in two strike counts, then he'd probably face fewer lefties with two-strikes to begin with. However, the point remains, the spike in Cole's platoon split vs. lefties is largely explained by his lack of success getting outs with his fastball in two-strike counts. In other words, he is not finishing off left-handed hitters with his fastball when he has two-strikes.

Interestingly, it is the fastball, not the slider that is the source of his struggles against LHBs. Overall, lefties are batting .290 against the pitch, compared to last year's .151 clip. However, only 31 total plate appearances have been resolved by the slider. That is all pitch counts, not just two strike counts. If his slider was getting outs at the rate it was last year, it would only save him four hits against lefties in total. The spike in average against the fastball in two-strike counts accounts for 14 additional hits. It's the fastball in two strike counts against LHBs, not the slider in all counts, that explains most of the uptick.

So, the question becomes what has changed with the fastball?

First of all, he is facing 2.1 percent more full counts against LHBs than a year ago. In these situations, one would expect a hitter to sit fastball and have greater success. While that hypothesis appears sound, it doesn't explain why he is a allowing a .350 BA on fastballs in full counts this year vs. .182 last season. It appears, then, that something is going on with the fastball itself.

Velocity isn't the issue, as there is only a 0.5 MPH drop from last season in two strike counts. Sequencing isn't the issue, as his two-strike pitch mix vs. left-handers isn't dramatically different from past years. In fact, he is throwing four ercent fewer fastballs.

That leaves us with location:

Here is his fastball heat map for fastballs with two strikes vs. left-handed hitters (via Baseballsavant.com):

2015: (from catcher's perspective)

2016: (catcher's perspective)

Last season, Cole's two-strike fastballs vs. lefties remained mostly up and outside, or lower middle. This season, the ball is often traveling middle up in the zone. Whether changing location explains the spike in left-handers success with two strikes is speculation at this point, but it could be part of the answer.

Here is what the batting averages look like in the different zones.

2015:

2016:

Cole is giving up two-strike hits against LHB with his fastball at a higher rate across all the zones this season. However, pitches middle up-and-in are a zone that hitters didn't touch (or didn't have the opportunity to touch) in 2015.

Another possibility is bad fortune. With such a small sample size, it could be that simply more balls are finding holes than last year. While this seems like the most likely answer to me, the decreased whiff rate and increased percentage of balls in play gives one pause.

Year	Whiff % with fastball vs LHB, two strikes	In-Play % with fastball vs. LHB, two strikes
2015	35	52.5
2016	24.6	60.7

Cole's strikeout rate is down across the board. He is getting eight percent less whiffs per swing on all sliders and four percent on all fastballs. The swing and miss stuff isn't there like in past years. It is possible that part of the drop-off is by design, however, as Cole continues to adopt the Pirates' pitch-to-contact philosophy.

So, what do we know? At first glance, Cole's platoon splits are the big reason for the dip from last year's elite level performance. However, zooming in on his platoon split reveals that the problem exists in a very specific context: i.e. fastballs thrown with two strikes. With two strikes, left-handed batters are hitting fastballs at a .328 clip compared to .100 BA last season.

The source of the spike in average doesn't seem to have anything to do with velocity, increased number of full counts or pitch sequencing. The only noticeable change is pitch location, with more fastballs coming in up in the zone and towards the middle-in half of the plate. However, he is giving up hits across all the zones, not just mistakes up and middle. A more in-depth look is needed to confidently blame poor execution for the increase in hits.

Of course, the more unpopular explanation could in fact be the answer: it may just be a really bad run of luck. If it is bad luck, then that might be a good thing for Pirates' fans, as it means there is no underlying physical or mechanical issues. On the other hand, it also means that last season's elite performance was pushed along by the same forces.

After tonight's game, in which he allowed 12 more hits over 6 2/3 innings and escaped allowing only three runs, Cole wouldn't take the bait when asked if a pitch-to-contact philosophy partly explained all the hits. He also seemed mostly pleased with his execution of pitches throughout the night. He did, however, express some frustration with what he called a "couple weird hits." In particular, he pointed to the two hits he allowed in the first inning which, incidentally, were two singles hit by two left-handed hitters in two-strike counts (one on a fastball the other a slider).

"It just seems like some weird luck sometimes," Cole said. "I had guys on first and second (in the first) and I hadn’t made a bad pitch yet. You can’t control stuff like that so you just have to continue to work hard. A lot of those situations we executed pitches, but just didn’t get rewarded."

Gerrit Cole's season would look a lot different if he was repeating the success he had with in his fastball in 2015 against LHBs with two strikes. It is those precise situations where the difference between last season to this season appears most vividly. It's not clear what is causing the spike in batting average, but location and bad fortune are the leading candidates. What we know is where this season's numbers are coming from. Watching two-strike fastballs to left-handed hitters more closely may lead us to an answer.