(I don't want to push the game thread down the page, so click through for the post.)
In postgame correspondence, reader Terry Benish mentioned something about Felix throwing with a lower arm angle. I decided to load up the videos from Opening Day and last night, and, uh, well:
Bam. Last night Dave and I speculated that Felix has a different delivery for his curveball than he does for his other pitches, and now we've got some visual evidence. At curveball release, he looks identical in the two pictures. At fastball release, though, he doesn't (it's the same for his two-seamer, four-seamer, and slider, but for the sake of saving space I didn't include those pictures here). On Opening Day his fastball and curve have very similar arm slots, allowing him to get on top of the ball, but in these screenshots from last night he's clearly dropping his arm for the fastball (and slider). It wasn't just yesterday, either; after checking a ton of video, he's been doing this for a long long time. Again, posting all those pictures would've taken up a lot of room, so I decided against it, but if you're skeptical it's all on the official website if you want to see for yourself.
Where Opening Day Felix came over the top for his fastball and slider, Since Then Felix has been throwing more across his body. Here's a good rule of thumb that any pitcher can tell you: if you want more vertical break, throw more overhand. If you want more horizontal break, throw more sidearm. I can't establish a direct cause-and-effect relationship between Felix's lowered arm angle and the loss of bite on his two-seamer and slider, but this definitely looks like a reasonable explanation. He isn't letting his fingers cut through the ball as effectively now as he was with his more overhand delivery, and at the same time he's missing the good break on his pitches.
If I'm Raffy Chaves, this is what I focus on more than anything else going into Felix's next start. Forget all that stuff about 'balance' and 'rushing' that came up in the newspapers the other day. Maybe this is why Felix isn't finishing his pitches well - there's an issue earlier in his delivery that's affecting the end of it. It is harder to get the same finish and snap with a lower arm angle. That's how you hang pitches and miss high. Felix needs to go back to getting on top of the ball. When Felix throws his bullpen tomorrow, Chaves needs to tell him to throw his fastball and slider from the same arm slot as his curveball. It might not be the answer, but it certainly looks like it could be.