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Patrick Corbin has never had a particularly good fastball. Even when he was able to dial it up to the 96-97 mph range, the results were never particularly great.

Opposing batters have hit .298 against his four-seam fastball and .301 against his sinker for his career, with ISOs allowed of .179 and .161. Even given the relatively low standards for fastballs around baseball, Corbin's has been especially whiff-averse, picking up a swinging strike on 6.2 percent of his four-seamers and 4.9 percent of his sinkers.

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In April, he was averaging 92.5 mph with his sinker (the primary fastball he uses) while maxing out at 95.7 mph; on Monday against the Brewers, he topped out at 92.6 mph. And this isn't a new thing either, as that was actually the hardest pitch he'd thrown since late-April. On average, his sinker has lost 3.1 mph from May to April, the largest drop in the league from one month to the next. It's the worst fastball velocity we've seen from Corbin since a lone start in September 2012:

This is obviously bad news, right? Here's the surprising thing: Not so far, at least.

Corbin was tagged for four earned runs Monday, however he had allowed just two before going out for the seventh inning. Before that, he had allowed just two runs in 11 innings in his previous two starts, and has allowed just 12 hits in 17 innings in May overall. If Corbin's declining fastball is a warning sign, it hasn't shown up in his performance.

And the reason why isn't hard to see: Corbin has been less fastball dependent than ever before. Given his previously documented issues with the pitch, it's no surprise that he's throwing it about half of the time.

(Note: Corbin has also almost entirely ditched his changeup, a pitch he fared even worse with throughout his career. He has only thrown four all season, per BrooksBaseball.net, a number so low it might well be a classification error.)

Corbin's slider has always been his best pitch, and he's pulling a Lance McCullers, using it in such a way that it might as well be his primary pitch:

Corbin threw the slider 36 times Monday, and he baffled opposing hitters, inducing 14 whiffs on 17 swings — a whopping 82.3 percent of the time. He has also introduced more of a slow curveball this season, using it about 11 percent of the time after never having it as part of his arsenal before.

All this is to say, Corbin's approach makes sense, and it works. Even with a significant drop in fastball velocity, we haven't necessarily seen a significant dip in production because he isn't using the fastball very much. The sample size isn't huge, of course, but Corbin has mostly kept rolling right along, striking out 29.9 percent of opposing batters of the three starts during which his velocity has declined. Velocity isn't everything.

That doesn't mean there is no reason to be worried, of course. If Corbin is proving he can be effective despite diminished velocity, that still isn't answering the more fundamental question: Why is his velocity down in the first place?

For his part, Corbin hasn't expressed much concern about the drop in velocity. And we haven't really seen much of a change in his release point so far, one of those tell-tale signs of a hidden injury.

So, if Corbin says he feels fine, and it's not impacting his performance, all's well, yes?

Probably. I can't say definitively, because, well … he's presumably not throwing his fastball 90 mph on purpose! Something's going on here. It might be something small and correctable, a mechanical hitch the Diamondbacks' coaching staff can identify and fix.

Or it could be something more ominous. Corbin has a reputation of being injury-prone, but he has actually only been on the disabled list once in his career when he underwent Tommy John surgery in 2014. He missed a season and a half as a result of that injury, but hasn't missed time since. The track record here actually isn't as bad as you think.

Still, this is about as glaring as red flags get. Typically, pitchers don't lose 3 mph off their fastballs for no reason. Maybe Corbin is fine physically, and he'll either revert back to his old self or continue to pitch with diminished velocity. As I said before, I think he can pitch effectively like this. The question is, how long can he pitch at all?

I know my co-worker Scott White isn't worried, and would gladly trade for Corbin, velocity be damned. I'm going to go try to work out a deal with him.