This post begins with a friendly reminder — specifically, that there are five teams in each of baseball’s six divisions. Given the noise around baseball for much of the offseason, one could be forgiven for thinking there were only four clubs in the American League East. Much of the chatter regarding the AL East this winter has centered around the formidability of the Yankees’ roster, the Red Sox’ (now successful) pursuit of J.D. Martinez, the imminent close of Baltimore’s competitive window, and the Rays’ sort of, kind of, not really teardown. It isn’t that the Blue Jays have done nothing — they’ve made several good trades and taken low-cost risks — it’s just that there have been a few more prominent stories and louder fanbases.

The most recent move out of Toronto continues the club’s offseason trend of reasonable, low-cost acquisitions. For a price of just $2.5 million, the signing of Seung-Hwan Oh — a player who, in 2016, recorded nearly three wins out of the bullpen — seems like a potential bargain.

Of course, he would not be available at this time of the offseason and at this price if he didn’t have some warts. He is coming off of a mediocre 2017 campaign, falling from one of the leauge’s top-10 relievers to barely replacement level. Of possibly greater concern is the fact that the Rangers nixed a potential deal after expressing concerns with Oh’s physical. Despite these warning signs, there is reasonable optimism for an Oh turnaround, one that would benefit the Blue Jays in either a playoff chase or as a deadline trade chip.

Upon coming over from the KBO in 2016, the “Final Boss” was a revelation. He mixed a strong fastball with a potent slider, even throwing in the occasional splitter to keep hitters off balance. His numbers were impressive: Oh struck out nearly a third of batters faced while walking only 5%. When Trevor Rosenthal faltered, Oh took over the closer role for a Cardinals team that fell a game short of the Wild Card.

For as good as 2016 was, 2017 was equally as bad. Oh’s ground-ball rate declined, his home-run rate spiked, and he struck out a third fewer batters. It all combined for a 0.1 WAR, down from 2.6 the year before, the seventh-largest single-year decrease in WAR for a reliever since 2001.

What happened that caused the deterioration of Oh’s performance? A cursory glance at the numbers, specifically the pitch values for Oh’s three main pitches, tells the top-level story.

Seung-Hwan Oh Pitch Values (Per 100) Season Fastball Slider Splitter 2016 1.7 2.2 0.6 2017 1.3 -1.1 -7.1

It seems that Oh’s fastball still remained a decent weapon in 2017, while his slider and splitter fell off the edge in terms of effectiveness. When you look at deeper numbers on the pitches, this narrative is borne out further.

Seung-Hwan Oh Pitches, 2016-17 Pitch Season Whiffs/Swing BIP % GB/FB AVG ISO Fastball 2016 29.0% 13.5% 0.9 .208 .088 Fastball 2017 26.5% 14.0% 0.6 .248 .133 Slider 2016 45.2% 16.3% 1.9 .164 .082 Slider 2017 28.9% 24.8% 1.0 .280 .151 Splitter 2016 42.2% 15.7% 2.7 .200 .000 Splitter 2017 30.0% 25.4% 2.0 .375 .333

We again see a fastball that backed up slightly, but sliders and splitters that were not nearly generating as many whiffs and endured more damage when being put into play. It’s easy to chalk this up simply to greater familiarity with Oh’s stuff among opposing batters. However, if we look at the velocity, movement, and release of his pitches, we see that Oh may be just an adjustment away from returning to dominance.

Oh’s velocity essentially didn’t change from 2016 to 2017, so the decay in his numbers doesn’t seem to be tied to that. However, he saw decreases in vertical drop from both his slider (3.01 to 3.27 inches) and splitter (4.49 to 6.24) in 2017. What caused this change in movement?

Unsurprisingly, Oh seems to have inadvertantly changed his mechanics. In 2016 (represented by the red points in the plots), Oh got more extension (5.77 feet in 2016 vs. 5.55 feet in 2017) on his slider and released it at a slightly higher point (5.46 feet in 2016 vs. 5.32 feet in 2017). The same was true of his changeup, which featured more extension (5.87 feet in 2016 vs. 5.71 feet in 2017) and higher releases (5.62 feet in 2016 vs. 5.5 feet in 2017) in 2016.

So basically, it looks like Oh stopped getting on top of his pitches, leading to less drop. This left more pitches up in the zone leading to fewer whiffs and grounders. If Oh manages to find his 2016 delivery, he may see his 2016 results return. Even amongst his 2017 results, there was reason for Oh to be hopeful. He lowered his average exit velocity (85.1 mph in 2017 vs. 87.5 in 2016), while his walk rate remained fairly similar. The Blue Jays have every reason to believe that Oh could return with a slight change.

A return to form for Oh would be a minor coup for a Blue Jays bullpen that lost two of its top members from last year. They still have Roberto Osuna, who put 3.0 WAR in 2017, leading a bullpen corps that was a top-10 unit last year. But Joe Smith signed with the Astros, while Dominic Leone went to the Cardinals in the Randal Grichuk trade. A pitcher like the 2016 version of Oh would provide the Blue Jays with one of the better setup/closer combos in baseball.

All this, of course, supposes that the Blue Jays contend in 2018. Should the depth of the AL East cause Toronto to fall behind the pace, a rejuvenated Oh would be attractive to contenders, while the going rate for relief pitchers would give the Blue Jays opportunity to add to a top-10 farm system.

Seung-Hwan Oh was not good last year. However, despite his poor performance, there was reason for optimism in his underlying numbers. Even more so, it seems like a small adjustment on Oh’s part could return him to his impressive debut season. Even if Oh ultimately becomes only a deadline trade chip for the Blue Jays, he provides baseball with a great comeback story opportunity and the Blue Jays with a low-risk, high-reward option out of the pen.