Darren O'Day's Surprising Splits

Once again, sidearm specialist Darren O'Day in the midst of another productive season for the Baltimore Orioles. Currently boasting a 1.08 ERA/2.90 FIP/3.27 xFIP pitching slash line and staying neck and neck with the likes of closer Zach Britton and ground ball specialist Ryan Webb for the Orioles reliever lead in fWAR—Britton currently sits a 1.0 fWAR, with O'Day and Webb not far behind at 0.9 and 0.8 fWAR, respectively—O'Day is also leading the bullpen with a 19.08 RE24, which is bested only by New York Yankees All-Star setup man Dellin Betances (24.20) in MLB.

What has gone somewhat unnoticed this season—if there's such a thing with sidearmers—is O'Day's ability to get lefthanded hitters out, something that is typically the downfall of pitchers of his ilk. Over his career, O'Day has a left/right wOBA split of .304/.251, a surprisingly respectable split, given his arm angle. However, this season, O'Day has one-upped himself, keeping righthanded hitters to a .246 wOBA and lefthanded hitters to a .241 wOBA.

Yes, Darren O'Day, righty sidearmer extraordinaire, is more effective against lefties than he is righties in 2014.

Compounding the confounding is O'Day's 2013 splits, which had saw lefties and righties hit at a .394 and .206 wOBA, respectively, a disparity typically seen (and accepted) from sidearmers. While many pitchers with O'Day's approach and style will often look for an additional weapon to counter opposite hand hitters, be it a another pitch or honing of their command of both side of the plate, it is exceptionally rare to see such a dramatic about-face in such short notice, even with the knowledge that O'Day's career splits aren't as eye-popping as his 2013 season's. However, O'Day did in fact add a little wrinkle to his repertoire in 2014, adding a changeup to his four-seam fastball, sinker, and slider mix, using it exclusively against lefthanded batters. While it would be easy to hoist the explanation for O'Day's suddenly superb pitching against lefties on the new pitch, the fact that he has thrown ten in total all season, most recently in mid-May (per Brooks Baseball), speaks to his success against lefties being a result of something else.

Speaking of Brooks data, let's look at some more, in particular, his career, 2013, and current season numbers with changeup data removed, to see if anything jumps out as a potential cause for O'Day's success against lefties:

Year	Pitch Type	Freq	Velo (mph)	Hmov (in.)	Vmov (in.)	H. Rel (ft.)	V. Rel (ft.)
2013	Fourseam	33.42%	87.32	-7.19	2.48	-3.25	3.53
	Sinker	19.54%	86.47	-7.71	-3.82	-3.21	3.31
	Slider	47.04%	79.77	4.51	1.23	-3.3	3.51
2014	Fourseam	32.00%	88.57	-8.01	3.39	-2.98	3.68
	Sinker	30.18%	87.85	-8.56	-3.67	-2.89	3.45
	Slider	29.68%	80.23	4.77	1.3	-3.04	3.56
Career	Fourseam	28.11%	87.5	-7.42	2.79	-3.06	3.61
	Sinker	35.08%	86.28	-7.15	-3.71	-2.93	3.33
	Slider	35.75%	79.12	4.56	1.23	-3.13	3.49

In terms of pitch selection, it looks like 2013 saw O'Day deviate mildly from his career averages, going less with the sinker in place of more sliders. This season, he has returned to a more balanced approach, throwing all three of his primary pitches (along with those ten changeups), with each pitch showing a little extra oomph to them, velocity-wise. Also, the sidearmer's release point (H. and V. Rel) is a touch higher vertically and a little closer to body body horizontally in 2014 compared to least season or over his career. This minor tweak has also added a little extra horizontal movement to his pitches (Hmov), with his four-seam and slider also seeing a little boost in movement this year.

Let's now turn our attention to what happens once O'Day releases the pitch:

Year	Pitch Type	Strike	Swing	Whiffs
2013	Fourseam	22.31%	50.77%	17.69%
	Sinker	27.63%	43.42%	6.58%
	Slider	33.88%	40.98%	8.20%
2014	Fourseam	20.43%	62.37%	18.28%
	Sinker	34.52%	40.48%	7.14%
	Slider	34.52%	35.71%	5.95%
Career	Fourseam	18.68%	54.50%	14.77%
	Sinker	28.57%	45.31%	5.44%
	Slider	36.18%	40.45%	8.28%

The extra wiggle and velocity seen from the four-seam fastball has been especially kind to O'Day in 2014, with the pitch generating more whiffs and swings than last year or over his career. This is combined with this season's improved ability to throw the sinker for strikes and get a few mores whiffs, with the slider apparently being thrown for called strikes, given the increase in strike percentage and concomitant drop in swing rate.

Batted ball data show similar changes in 2014:

Year	Pitch Type	GB	LD	FB
2013	Fourseam	3.85%	4.62%	6.92%
	Sinker	10.53%	1.32%	7.89%
	Slider	6.01%	1.64%	3.83%
2014	Fourseam	3.23%	5.38%	4.30%
	Sinker	22.62%	1.19%	2.38%
	Slider	2.38%	4.76%	2.38%
Career	Fourseam	2.72%	4.24%	6.28%
	Sinker	16.46%	2.99%	5.58%
	Slider	3.87%	2.40%	5.47%

The sinker again provides O'Day a lot of success in the form of ground balls and a drop across all three pitches in fly balls rates. However, it does appear to possibly come at the cost of some bite to his slider, as the drop in ground ball rates to go along with an increase in line drive rate—a crude measure of how hard a ball is hit—show that the slider has maybe lost a little magic this season. However, these purported decreases in effectiveness of the slider could simply be a result of O'Day flipping the pitch over in first pitch counts, working backwards to get ahead in the count. Some of this notion if reflected when looking a first pitch slider percentages, with 2014 seeing him throw a slider first pitch 47% of the time; this pales in comparison to his 2013 average of 59.5%, but is up from his career average of 40% sliders in 0-0 counts.

Finally, let's look at pitch locations between 2013 (left) and this season (right). First, the fastball:

...and the sinker:

...and the slider:

For the fastball, we see O'Day pounding the upper part of the zone with the rising heater, but in 2014, he's doing so with better command. Compared to 2013, this season has seen his fastball stay out of the heart of the plate and maybe more importantly, away from a lefty's power—down and in. With the sinker and slider, it's a similar story; better strikes and fewer mistakes making their way over the plate, with pitches that miss doing so out of the zone and away from a lefty's power.

While the odd splits and ridiculous levels of success against lefties will probably be a fleeting thing for O'Day, we do see some changes to his approach that show some promise that he'll be able to face lefties effectively—better command of the strike zone with his offerings and improved ability to change planes and eye levels of hitters with his fastballs and slider. His willingness to throw a changeup to lefties, while a work in progress, is also an encouraging development and could lend itself to eventually becoming a more relied upon weapon to neutralize lefties. For now, better control, a slight change in arm slot, and an uptick in velocity combined with a willingness to work backwards should help keep O'Day atop the AL reliever leaderboards in a number of categories and more importantly, keep lefties as well as righties off of the base paths.

Data courtesy of FanGraphs and Brooks Baseball.