What happened to Drew Pomeranz on Tuesday?

The trade in which the Red Sox received Drew Pomeranz in exchange for Anderson Espinoza was one of the more controversial deals in recent Red Sox history. I don’t need to rehash the arguments on both sides — all of us endured them recently enough to remember — but it’s worth mentioning that how the new starter performed this year would go a long way towards how we viewed the deal in five years.

His Boston career got off to a rocky start, but after that he started pitching like a guy who was worth a top-25 prospect. Over a seven start stretch from early August through early September, he put up a 2.76 ERA with 44 strikeouts and 14 walks over 42 innings while allowing a .700 OPS. There’s no doubt he is a big factor in the rotation suddenly looking like a legitimate postseason group.

Of course, his last outing did not go so swimmingly. He was facing a great Orioles lineup, to be sure, but fans and the team rightfully expect more out of him. He lasted only two innings in the outing (he started the third, but did not record an out), allowing five runs on four hits and two walks while striking out three. The bullpen picked him up and gave the team a chance to win, but it was certainly a crushing outing for the lefty. The question is: Was this just a blip, or is it something to worry about.

There are a few different reasons why Pomernaz could’ve struggled the way he did. Some have speculated that it is a sign of fatigue as he heads down the stretch of a long season. Others point to the extra rest he had before hitting the mound. And, of course, there’s the very real possibility that it was simply a bad start, which is a thing that happens in baseball. Let’s take a deeper look at each of those possibilities and see if any has more merit than the others.

Fatigue

This would be the most worrisome factor for the Red Sox. Much has been made of Pomeranz’s workload since the trade was made, as this is his first full season as a starter. He’s already tossed 160-2/3 frames this year, which exceeds his previous career-high of 147-1/3. It’s even more of an increase when you consider that most of those 147 frames came in the minors, and one would think pitches against major-league opponents are generally more stressful.

The first and most obvious test for fatigue would be velocity. Brooks Baseball charts velocity in each game, and there’s not much visible change on his three major pitches. His cutter has dipped a bit, but his fastball actually ticked back up against the Orioles.

So, judging purely by velocity there is little reason to think fatigue is at play. Of course, it would be simplistic to think that’s the only way a tired pitcher would reveal himself. Command is another, and if you watched Tuesday’s game you know that was off. Another indicator could be release point. Pomeranz’s vertical release point, per Brooks Baseball, has not seen any significant recent change. This would probably the best test. However, his horizontal release point has.

As you can see, he has started to open up more over his last few starts. This may not be caused by fatigue -- it’s impossible to say from the outside — but mechanical changes can be a sign of this. I would say the evidence leans more towards no than yes overall for fatigue, but there’s a small case for it.

Extra Rest

This was a common concern I heard after the start, and it wasn’t one I had considered. If you remember correctly, Pomeranz’s other horrible outing for the Red Sox came in his first outing with the team, and that also came on extended rest. So, I looked at his splits on his Baseball-Reference page to see if there’s a trend here. This year, there certainly is.

As you can see, there is little difference in the K/BB numbers, but there is a clear difference in how opponents have been able to square Pomeranz up when he’s had extra rest. We are dealing with a five start sample, though, so this data is questionable at best. To get a better sense, let’s look at his career numbers. Note that these are, of course, ignoring any relief appearances.

Using the 17-start sample in his career, Pomeranz doesn’t appear to have much of an issue with starting on longer rest. Now, the fact that he’s been shuffled between the bullpen and the rotation muddles this a bit, but I’d still trust the larger sample. Like fatigue, I’d be inclined to lean towards no here but there is enough evidence that doubt creeps in.

Random Bad Start

Honestly, I don’t think there’s much reason for big analysis in this section. We all watch baseball a lot, and realize it’s a weird game. Sometimes good players are bad and bad player are good. It happens. Still, to illustrate this point I’ll look at a couple of similar pitches in terms of performance this year and see if they’ve had starts like this. To define “similar,” I’ll look at Baseball Prospectus’ DRA-based WARP, because that’s my favorite.

It’s an arbitrary decision, but whatever. Pomeranz finds himself sandwiched between Masahiro Tanaka and Cole Hamels by the measurement.* We’ll judge starts by Game Score. Again, this isn’t perfect, but it’s good enough to illustrate the point. Pomeranz’s last start registered a Game Score of 29, which was his second start less than or equal to that mark. Tanaka has had one such start. Hamels has had four. I could go deeper, but I don’t think it’s necessary. Bad starts happen.

*Can we just take a second to realize how crazy that is? It’s almost certainly a bit aggressive, but Pomeranz has been super good this year.

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As often happens to me, I can’t bring myself to come to a strong conclusion here. I will say that I’d certainly lean towards this simply being a bad start, as that was mostly my default position here. I would probably rule out the fatigue factor, though the mechanical change in his last few starts has my interest piqued, at least. The extra rest theory is also interesting, as it’s been a trend for him this year and has been a common thread in his two horrendous Red Sox outings. As for the team, they had better hope it’s one of the latter two, and preferably the last reason. If they want to make a deep run this year, they’ll need Pomeranz near his peak form.