Why has Santiago Casilla been so bad lately?

Santiago Casilla has been bad this year.

I know, I know, the McCovey Chronicles enfant terrible is stirring up trouble again, but dammit, I have to stand up for my beliefs. And sadly, in 2015, Casilla has been a stain on a bullpen that itself seems to be about half stain. By ERA, this is by far Casilla's worst season since a dashing young rogue named Jairo Garcia made the A's wonder "Why are we paying this person to throw baseballs?"

So what's gone wrong? It's not his velocity – his fastball is down a little from last year but pretty similar speed-wise to the three years before that. It's not his strikeout rate – he's striking out more guys than he has since 2010. No, it's the everything else. Everything else: it'll get ya every time!

Casilla's biggest problem this year has been facing left-handed batters. While he's doing fine against righties – they're hitting just .218/.292/.267 against him, for a wOBA of .256 – lefties have crushed him to the tune of .328/.429/.636 for a .458 wOBA. To put it another way, right-handers against Santiago Casilla are hitting worse than Angel Pagan, while left-handers against Santiago Casilla are hitting better than Mike Trout.

Now, Casilla's always had platoon splits, but they've been relatively minor. Here, I made a chart, and then I put a stegosaurus on it because stegosaurus was the second best dinosaur:

Something about 2015 is different from the other years, but I just can't put my finger on it. Maybe that line just wanted to get as close as possible to the dinosaur. Really irresponsible of me to put that there and possibly ruin the Giants' season.

Beyond the L/R splits, the other red flag that seized control of Redflagistan and raised its red flag above the Palace Of A Thousand Red Flags is Casilla's home run rate. Other than in 2012 (when a lot of his problems could be explained by a blister that dogged him for months), with the Giants, Casilla's been consistently under .5 homers per nine innings, but this year he's at 1.14. This is likely to regress (in a good way!), if only because he's giving up home runs on a far, far greater percentage of fly balls than he ever has before.

But this too is part of the lefty-righty splits; left-handers are, absurdly, averaging one home run hit against Casilla for every four innings he pitches against them. Right-handers have homered once against him in 23 innings.There is nothing in Casilla's career to suggest this should be the case, so it's reasonable to assume this won't continue. Baseball, of course, isn't reasonable, and if Casilla continues making all lefties look like a slightly better Miguel Cabrera, then I'd kindly ask you to forget the entire last half of this article so that I don't look stupid.

So what's the reason to think that these trends will reverse themselves, other than the new logical fallacy I just invented called "appeal to history"? First off, most of Casilla's other numbers aren't hugely different. His K/9 and BB/9 are both up, but if you look at percentage of batters instead, the strikeouts are still up but the walks are pretty consistent. Batters are making the same amount of contact against him as they always have, though slightly more of it is hard hit. His horizontal and vertical movement is the same as it's always been, his horizontal and vertical pitch location haven't changed much either, and he's not grooving a ton of pitches.

On the other hand, Casilla is giving up fewer ground balls and many more line drives. His BABIP is up to .330, which is very high, but that could easily be driven by a higher line drive rate. Hitters are swinging at his pitches less, and those pitches are also in the strike zone less, leading to more hitters' counts and more gnashing of garments and rending of teeth. And then there's the plain fact that FIP and xFIP have never liked Casilla, and he could finally be regressing (in a bad way!) towards the mean.

That was the hedging paragraph, where if he keeps being bad despite all the evidence I've shown that he should be fine, I can claim that I kinda saw it coming. It's a neat trick.

Will Santiago Casilla continue being bad? I'm not a fortune teller, and baseball wouldn't be any fun if we knew these things in advance. But if I have to give a prediction: I don't think so, but maybe. He should be a pretty good pitcher. So far, he hasn't been. Let's hope that reverses.