If you wanted a microcosm of the 2016 season, it was the utter implosion of Shelby Miller after becoming a Diamondback. From an All-Star in 2015, his mechanics became so bad, he was literally scraping his knuckles on the ground with his follow through, which required a DL stint. That didn’t fix things, and he ended up being optioned to the minor-leagues at the All-Star break, having gone 2-9 with a 7.14 ERA. That was the worst first-half ERA of any NL pitcher (min 14 starts) since Hideo Nomo in 2004.
Things didn’t exactly improve greatly on his return.