Darren O'Day's Small Change in Slider Use

Darren O’Day has been an integral part of the Orioles bullpen since he was acquired prior to the start of the 2012 season. From 2012 through 2015, he pitched to an ERA of 1.92 over 263 innings, and was worth 4.9 wins according to Fangraphs. That’s really good. And as Matt Kremnitzer pointed out in a post before the season, O’Day does even better according to Baseball Reference’s version of WAR, which is based on run prevention rather than FIP numbers. Baseball Reference has O’Day at 9.6 WAR over that same time period. That’s outstanding.

Following that run of dominance, O’Day submitted an injury filled stinker of a 2016 season (at least in comparison to his lofty standards) in the first year of a 4 year, $31 million deal. After 22.1 innings pitched in 2017, O’Day appears to have returned to his role as relief ace, non-closer division. While his overall numbers may not match what one may think of when they think “relief ace”, much of that is a result of a couple bad outings at the very beginning of the season. That 3.63ERA? Five of the nine earned runs he’s given up came in his 2nd and 3rd appearance. That 12.0% walk rate? Five of his 11 walks came in his first two games. That 66.4% left on base rate? In all but 4 of the 23 games he has pitched, he has had a LOB% of 100%, and 2 of those 4 games were (you guessed it) his second and third appearance of the season. So after a couple of rough outings (mostly the appearance April 9th), O’Day looks (for the most part) like the O’Day of old.

Darren O'Day (photo via Keith Allison)

But he’s not exactly the O’Day of old. Yes, he’s getting ground balls (50.0%) at the highest rate since 2008, but it’s his slider caught my attention. According to the linear weight pitch values at Fangraphs, O’Day has thrown the 8th most effective slider in the majors this year (minimum of 20 innings pitched). While his slider Pitch Value of 6.7 runs above average is not a career high (yet), his wSL/C (standardized Pitch Value per 100 pitch) of 3.82 runs above average would be a career high by 1.67 runs. So O’Day’s slider seems to be working more effectively than ever, but according to Brooks Baseball, it’s not how much he's throwing it (overall usage has essentially been the same the last 4 seasons). And it’s not the movement on the pitch either, as both the vertical and horizontal movement appear to be trending in the wrong direction so far this season.

So how has it been so effective? It could be from a change in use of the pitch, particularly to left-handed batters. While O’Day has not been terrible against left handed batters over the course of his career (wOBA against of .299), he’s definitely been better against right-handers (.248 wOBA). In 2017 however, he’s so far managed a reverse platoon split, holding left handed batters to a wOBA of .212. Now, he’s only faced, 36 left-handed batters and they have a .177 BABIP against him, so he’s very likely gotten the benefit of some good fortune. However, he’s also striking them out 11.1% more often than he is right-handers while inducing more soft contact from left-handers than ever before (up 13% from career levels).

I mentioned earlier that O’Day’s overall use of the slider hasn’t really changed this year. However, if you only look at his slider usage versus left-handers, you’ll see almost a 7% increase from last year.

Darren O'Day Pitch Use Versus LHB (via Brooks Baseball)

But he’s not only throwing more of them to left-handers, he’s throwing them much more early in the count, as you can see from tables below.

Darren O'Day Pitch Usage from 2008 to 2016 (via Brooks Baseball)

Darren O'Day Pitch Usage in 2017 (via Brooks Baseball)

Combine that with the fact that O’Day is throwing that slider against left-handed batters for strikes at a rate almost 16% higher than he previously has during his career, and we potentially see a deliberate adjustment combined with successful execution.

Darren O'Day Pitch Outcomes Versus LHB from 2008 to 2016 (via Brooks Baseball)



Darren O'Day Pitch Outcomes Versus LHB in 2017 (via Brooks Baseball)

Now it’s entirely possible that this is all small sample noise and that this was not a deliberate adjustment, just the whims of natural variation. We are essentially looking at only 1/3 of a relief pitcher’s season, boiled down even further to splits within that relief season. However, the appearance of O’Day’s slight change in the usage of his slider to left-handers combined with the fact that he’s throwing it for more strikes has not only been interesting, but it has also so far been effective for him. And whether or not this was by design or just a coincidence, O’Day is once again a key member of the an Orioles bullpen that will need to carry the load for a sub-par starting rotation. Here’s hoping he can keep it up, because he’ll likely need to for Baltimore’s season to be successful.