It is not uncommon for a retired pro athlete to attempt a comeback in their sport.
Plenty of players have initially planned to call it quits only to backtrack that decision because either a team came calling or the player realized they still had the desire to keep playing.
In most cases though, these types of efforts are reserved for when a player just announced their retirement or has only been away from the game for a year or two, like Jay Cutler and Marshawn Lynch in the NFL last season.
Rick Ankiel is clearly a different breed.