I think we’ve known since, oh, he debuted that Jered Weaver is capable of over-performing his pure stuff. He doesn’t blow anyone away, and he’s never blown anyone away, but he’s been terrific nevertheless, in part because of his home stadium but in bigger part because of something about his delivery. At least, that’s the presumption. Weaver appears to be the deceptive sort, and deception can be part of the recipe for a top-of-the-line starting pitcher. It’s a hard thing to teach, and a hard thing to recognize, but a wonderful thing to possess.

So, Weaver’s been something of a smoke-and-mirrors kind of guy. Because of that, he’s been hard to project –what’s the aging curve for a pitcher’s deception? But Weaver’s 32 years old in a couple days, and there’s evidence that there is indeed something missing for him. Check out his in-zone and out-of-zone swing rates over the PITCHf/x era, even including the relatively unreliable 2007 set:

This year, Weaver’s in-zone swing rate was right on his career average. However, his out-of-zone swing rate was lower than his average by five percentage points, dropping a little more than five percentage points from last season. For pitchers between 2013 and 2014 who threw at least 75 innings, Weaver’s O-Swing% drop is the greatest, and overall he posted the fourth-lowest O-Swing% in baseball given a 75-inning minimum. He was less than one percentage point away from last, and, interestingly, three of the four lowest rates were posted by Angels. C.J. Wilson saw a similarly big year-to-year drop, but he’d been around this level before, and he also struggled with his command. Hitters don’t swing as much against wilder pitchers.

I don’t know what this means, exactly, in that I don’t know why this happened, but this happened. And it’s not a good thing for Weaver, because he’s been a limit-quality-contact type, and it doesn’t help those pitchers to have hitters focusing more on the strike zone. According to Baseball Savant, last year, 57% of balls in play against Weaver were in the zone. This year, that went up to 60%, and while that’s a small difference, little changes power the big changes. It’s not unlike the difference between a .300 OBP and a .330 OBP — baseball is all about seemingly marginal differences.

We know by now that Weaver is consistently going to beat his FIP, because of the fly balls and the pop-ups. But maybe this is the only trend to know:

Jered Weaver isn’t a big strikeout pitcher, and he’s coming off a league-average walk rate, and now he’s looking something like a league-average starting pitcher. His K% – BB% has declined four straight seasons, as his fastball has lost more than three miles per hour, and while the rest of his pitches have been less affected, something else about Weaver just isn’t the same. He’s not as deceptive as he used to be. He remains deceptive enough, and he’s blessed with a potent supporting offense, but where does Weaver go from here? Will he get even less deceptive? Will he identify something to change to gain an edge back? How many more years does Jered Weaver have, if hitters are consistently less willing to chase him out of the strike zone?

I know better than to try to predict Jered Weaver’s career death. I know, though, that I’m more worried about reduced deception than about reduced velocity. Weaver’s game was never about velocity. It was about confusing the hell out of guys, and lately guys have been considerably less confused.