Let's somewhat arbitrarily use Doug Fister's 13th start - July 7th, against the Royals - as the splitting point.
Through July 7th: 75.6% fastballs
After July 7th: 65.4% fastballs
Through July 7th, Fister had 39 strikeouts in 84.1 innings. Since July 7th, Fister has 38 strikeouts in 50.2 innings. That's a far more acceptable rate, and you have to assume that it has at least something to do with the fact that he's been throwing fastballs less often than he was earlier in the year. Only once in Fister's last nine starts has his fastball rate exceeded 75%, after doing it nine times in his first 13.
Is it a meaningful change? We'll see. Is it a change at all, or just a statistical blip? We'll see. It is interesting, though, to see Fister suddenly striking some hitters out, and it makes me more confident in his ability to keep getting starts and doing his job without the whole sky falling down on his adorable little repertoire.