Exploring David Robertson's second-half struggles

David Robertson has spent the second half turning into the reliever version of James Shields. Not in the sense that he’s a diminished version of what he used to be, but that the White Sox are probably stuck with the last two years of his deal, unless they want to include a fair chunk of change.

He blew his second save in as many games to the Royals on Wednesday, and his fourth in eight tries during the second half, during which opponents are hitting .268/.348/.610.

The good news? He isn’t battling the tell-tale signs of aging as he’s throwing just as hard as he did last year.

The ... not good, but explicable news? He missed the last series of the first half with a strain in his upper left leg. Robertson called the point of the injury "a bad spot," and while he was probably being conversationally general, the hip does sound like a bad place for Robertson to get hurt, as he relies on supreme extension coming off the rubber. From a Tom Verducci story several years ago.

Imagine if Robertson moves the pitching rubber 14 inches closer to home plate every time he pitches. That's the kind of advantage he gains over the average pitcher by releasing his fastball with so much extension. The radar gun (and Trackman) clocks Robertson's fastball at an average of 93 mph. But because Robertson shortens the distance between his release point and home plate, his "effective velocity" is 95 mph. It looks like 93 but gets on a hitter like 95 -- thus the illusion of "hop."

There does seem to be a shift in his release point, both vertical and horizontal, around the time of the injury. Considering Robertson doesn’t rely on extreme velocity, it makes sense that any kind of reduction in "hop" could make him quite a bit easier to see (the movement on his cutter is also down in the second half).

We can only take so much solace in attributing his problems to health, though. He’s 31, so injuries aren’t as easy to brush off. Beyond that, his command has been off all year. He’s walked 12.2 percent of the batters he faced, which is up from 5.2 percent last year. One would expect some regression from the latter number, as it was a career low for Robertson. He spent the first four years of his career with a walk rate in that neighborhood, so it’s not unprecedented.

The problem is that 1) it’s been fairly consistent since early May, and 2) it’s paired with one of his lowest strikeout rates. That isn’t unprecedented either, but it’s what he did during his last non-elite year with the Yankees in 2010:

• 2010: 3.82 ERA, 26.0 K%, 12.1 BB%, 0.74 HR/9IP
• 2016: 4.18 ERA, 25.9 K%, 12.2 BB%, 1.14 HR/9IP

He still has his trademark reverse splits, but he hasn’t been overwhelming to lefties or righties this year, and the location of his cutter seems to be the big problem. It’s spending more time over the middle of the plate, especially to righties:

His command has also been more vague against lefties, which is perhaps why he’s given up four homers to them this year, which is as many as he gave up to them over the last four years combined.

If I had to guess, the injury is hampering him more than he is letting on.

Robertson was slowed by a left leg strain before the break, but Sox manager Robin Ventura said he hasn't let on if that affected him.

"Arm-wise and velocity-wise he's where he was, just not quite as sharp," Ventura said. "The swings lefties are getting on him, maybe the cutter isn't as big as it has been and burying it inside.

It doesn’t explain everything, but I’m guessing the awful version we’ve seen increasingly frequently stems from this. It’s either that, or his decline has started by seizing his elite command, and he was somewhat lucky to put out as many fires as he did in the first half.

In the meantime, Zack Burdi was promoted to Charlotte, as a late-season arrival in Chicago still seems well within his reach. It doesn’t have the urgency it once did, as he’s not trying to give the Sox another interesting arm for a wild card chase, but it’ll still be significant if he’s part of a high-leverage restructuring that diminishes Robertson’s role.