Earlier today we took a look at Felix and saw that, contrary to popular belief (in some circles), throwing more fastballs did not increase the effectiveness of his offspeed stuff last season. Quite the opposite turned out to be true. As his fastball frequency climbed, his swinging strike rates dropped for both his fastball and his secondary pitches, and along with them went his K/BB. Based on this information, it seems Felix was at his best when mixing his pitches around 55/45 or 60/40, and that 2008 represented a step in the wrong direction with respect to his development.
A point was raised by DCMariner in the comment thread that perhaps these numbers were reflecting an underlying trend where Felix would throw more fastballs when he didn't have his best offspeed stuff. Makes sense - if you don't have a good feel for your slower stuff, you're more likely to stick with your harder stuff. I thought it was an idea worthy of further investigation, so I went back to the spreadsheets and blah blah blah here are the results:
|FA% > 70
|FA% < 70
Looking at that table, I'm not seeing any significant differences in velocity, horizontal movement, or vertical movement for any of Felix's pitches. His changeup is a little bit faster in the upper group, but we're talking about a difference of less than 0.7%, which may not even be real. It's possible that Felix was throwing more fastballs because he didn't have a good feel for his offspeed stuff, but if that's true, there's no indication here. His slider, curveball and changeup look pretty much the same.
|FA > 70||FA||64.8|
|FA < 70||FA||63.7|
Here we see that, when Felix is throwing more fastballs, he's throwing it for more strikes (11 more strikes per 1000 pitches, to be precise), while his offspeed stuff misses the zone just a little bit more. This might be a sign of having a better feel for his fastball, but then the differences are slight, and it could also be a sign of using his breaking pitches as strikeout stuff more often when he's building more off of his heater. (That is, he may have missed the zone a little more often on purpose.) So, again, nothing definitive.
I'm not going to sit here and try to make the case that, by throwing fastballs more often, Felix makes all of his pitches worse. The numbers may lean in that direction, but they don't prove anything, and there are more variables to take into consideration than I can count. No, what I'm trying to say instead is that, at least as far as 2008 is concerned, there's no evidence that throwing more fastballs in any way helps Felix achieve more success. The numbers suggest that he's at his best when he's more evenly mixing his pitches, and absent any evidence to the contrary, I think it has to be worth giving a go. He won't always have a good feel for his offspeed stuff, but it's not like he always has a good feel for his fastball, either, and more important than the way Felix feels on the mound is the way the hitter feels at the plate.
Mix your pitches, Felix. A better mix, with less predictability, can take you an awful long way.
Related but separate note: in the last thread, johnbai mentioned game situations, and the idea that Felix is more likely to coast on his fastball when there's less pressure on his shoulders. Seemed like a good thing to check out, so here's a chart showing his fastball frequency plotted against pLI (a player's average leverage for all game events, available on Fangraphs):
There's a correlation there, but it's a pretty weak one. So while game situation does play a role in determining Felix's pitch distribution, it's far from the only factor.