I'm too young to remember Steve Blass but he is a negative legend. In 1971, he spurred the Pirates to a World Series title with two complete game gems against the Baltimore Orioles in the highest-pressure games imaginable: game 3, down 0-2 and game 7 on the road. In 1972, he went 19-8, 2.49 ERA, 249.7 IP, 84 BB, 117 K -- the best season of his career and he was only 30.
In 1973, he went in the tank. Blass could no longer find home plate: 84 BB in 88.7 IP (same as '72 in 161 fewer innings), 12 HBP (3x the '72 total), 9 wild pitches (6 in '72) and an ERA of 9.85. The Pirates lost their hold on the NL East, Blass lost his career and his inexplicable decline is now "Steve Blass disease".
In 2000, Rick Ankiel was a phenom for the Cardinals. He pitched like Kerry Wood, but left-handed. He went 11-7, 3.50 with the second-best K/IP ratio and second-best hits/IP ratio in the NL. He started game 1 of the divisional playoffs against the Braves. He went through the first two innings without much incident and the Cards gave him a 6-0 lead. In the third, he set a record by throwing 5 wild pitches. The lead dissipated, the Cards yanked him but started him in game 2 of the NLCS against the Mets. Again Ankiel honked: wild pitches, walks galore, and the 20-year old star-to-be was suddenly a bust.
Ankiel's troubles continued in 2001, he was sent to the low minors to straighten out, but he could not, then his elbow gave out.
Today, Ankiel is trying to come back once again. But after an abortive attempt at pitching, with frustrating and erratic results, he's decided to harness the rest of his athleticism and try something else: playing the outfield. Details in the story linked in the title.