Let’s get the horrible, cheesy joke out of the way, because I can’t help myself and have zero impulse control: lately, with Koji Uehara, it’s been more #HangHeadCity than #HighFiveCity. Okay, that’s out of the way, and I’m sufficiently embarrassed. In all seriousness, though, Koji has been pretty horrible lately. We’ve definitely been spoiled by his consistent, characteristic dominance throughout the past year and a half, so to see him sputter sets off alarm bells.

In his last six appearances, Koji has gone 1-3, with three blown saves and
zero saves. He’s only pitched 4.2 innings, and he’s given up 14 hits, 10 runs, and of the 13 fly balls he’s given up, four have left the yard (a HR/FB% of 30.8). He’s also allowed six line drives, whilst only inducing 3 grounders. It’s taken Koji 121 pitches to get through 4.2 innings over six games. In short, he’s a mess.

His nadir was arguably Thursday night against the Yankees (although, one could make an excellent case that his outing against Seattle on August 22nd was even worse). He was called upon to save the game for the Red Sox, but instead, he imploded. He gave up a solo shot to Teixeira on six pitches, which tied the game up. He then gave up a rocket of a line drive by Brian McCann that fortunately found the glove of Yoenis Cespedes. He took the count full against Chase Headley before allowing the walk-off home run. He threw 16 pitches and only induced one swinging strike. Not only was this loss demoralizing in the general sense, but it also robbed the Sox of their spoiler status. If the Sox won’t make the playoffs this year, the least they could do is make sure the Yankees and Rays are excluded also.

So what’s going on with Koji? It isn’t entirely clear, as his heat maps don’t show anything too out of the ordinary. However, it does seem like he might be having some difficulty with his splitter. In this six game stretch, his splitter has lost a bit of dip and dive and is hanging up a bit more than it has been on average this season. From opening day to August 15th, Koji’s splitter has had 4.3 inches of vertical movement. From August 16th until September 4th, his splitter has had 4.77 inches of vertical movement. That little extra bit of loft might be contributing to his opponents’ sudden power surge.

Additionally, his splitter has less horizontal movement, which is obviously part of the deception that induces swinging strikes. From opening day until August 15th, the horizontal movement of Koji’s splitter was -7.94 inches. From August 16th until September 4th, the horizontal movement on his splitter has dipped to -7.57 inches.

This may not be a significant discrepancy, but Koji lives in the strike zone, so he leaves himself very little wiggle room. Negative horizontal movement values indicate that a pitch is moving away from left-handed batters; conversely, pitches with positive horizontal movement values move in towards left-handed batters. As you can see above, Koji’s splitter has edged ever so slightly in a positive direction on the horizontal plane, thus making the splitter a bit more vulnerable to left-handed batters, as the ball moves further from the outside perimeter of the strike zone and closer to the heart of the plate. Incidentally, and perhaps unsurprisingly, the two home runs Koji gave up on September 4th came against two switch hitters, batting left.

These are small values, yes, but not insubstantial. FanGraphs’ pitch type linear weights, or “pitch values,” reinforce the obvious ineffectiveness of his splitter. Prior to this rough patch, Koji’s splitter has saved 9.8 runs, or an average of 2.6 runs per 100 pitches, near elite values for a reliever. Before his rough patch, Koji’s splitter saved more runs than the splitters of Jeff Samardzija and Homer Bailey combined (obviously, they have much wider arsenals, but both pitchers rely a fair amount on their splitters). Over his last six games, however, Koji’s splitter has cost the Sox -3.9 runs, or an average of -7.61 runs per 100 pitches. Frankly, it’s been a pretty garbage pitch, lately.

I don’t think Koji is done, by any means, but it is worth nothing he has lost 1 MPH on his four-seamer and his splitter, which is not unusual, considering his age, but it might be a contributing factor to his recent ineptitude. I feel confident that Koji might have just temporarily lost his feel for his bread and butter pitch, and I anticipate he’ll adjust and bounce back, but one wonders whether the Sox should have traded Koji at the deadline, too. It’s more than likely we’ve seen the best of what Koji Uehara has to offer; all that remains to be seen is how much more value he has to offer as he encroaches upon age 40.

(All stats courtesy of Fangraphs.com)