It's conceivable that you could have positive or negative variance in how your contact and pitch recognition components turn into strikeouts. Maybe Rizzo's actual strikeouts for one of the years aren't lining up with his strikeout peripherals, so to speak. It'd be neat to test if some sort of xK% was more predictive than actual K%.
K% O-swing% Z-zwing% Swing% O-contact% Z-contact% Contact% Zone% SwStr%
League average 20% 31% 65% 46% 66% 87% 79% 45% 9%
Rizzo 2012 17% 35% 68% 50% 64% 91% 81% 46% 10%
Rizzo 2013 29% 31% 66% 46% 57% 93% 79% 44% 10%
(with the exception of SwStr%, these all come from the PitchFX tab on Fangraphs, which has slightly different values than the other tab that has the same stats that I believe are hand-recorded by one of the stats services). Why was Rizzo better than league average at avoiding K's last season? It seems to be just that he was swinging at more pitches than average and thus ending the PA with a BIP. This year, he's swinging at fewer pitches, while making more contact in the zone and less contact out of the zone. His LD% has also gone down from 24% to 16%. So his K's this year are a combination of taking more pitches and failing to drive the pitches he's making contact with, presumably fouling more off, which combine to cause him to get into more 2-strike counts. His inability to make contact at pitches outside the zone are causing him to get wiped out by those 2-strike counts more often. When you look at his batted-ball data this year, you get a big drop in line drives and even a big drop in ground balls, but a big rise in pop-ups and fly balls (combined for 37% of his BIP last year vs. 56% this year). So we've got Law reporting that it seems like he's getting his hands low and loading slower. We've got an inability to consistently put the ball in play earlier in the count. We've got a major increase in fly balls and pop-ups. Those all seem to work together, so I'm going to take it as true that he's developed some sort of mechanical hitch that he'll need to either consciously fix or just work his way out of.