What are some notable baseball careers that started off HOF worthy only to derail badly.

First thought that comes to mind is Hanley Ramirez. People forget he was a top 2-3 Fantasy pick for a 3 year span. His first 5 years in the league were pretty damn good.

2006 - .292 Avg 17 Hrs 119 R 51 Sbs ROY winner
2007 - .332 Avg 29 Hrs 125 R 51 Sbs
2008 - .301 Avg 33 Hrs 125 R 35 Sbs
2009 - .342 Avg 24 Hrs 101 R 27 Sbs Batting champ
2010 - .300 Avg 21 Hrs 92 R 32 Sbs

5 yr avg .313 Avg 25 Hrs 112 R 39 Sbs

Playing for the marlins and batting lead off for a time, his RBI numbers weren't so high. Also in 2007 he was 1 Hr away from the 30/50 club, which has only been done twice in MLB history.

He went on to play 9 more seasons hitting above .260 just three of those seasons with 147 hrs. Around 2010 or so he got huge and lost his speed as well.