Toughest sport to make it as a pro? I'd say basketball. So many kids want to make it big in the US, but they're competing with tons of other players around the world for a spot on one of only 30 teams, with only 13 active roster spots on each team. There are D-leagues and various FIBA leagues in other countries too, but making it to the NBA as a pro is the goal, and it's tough to even get drafted with only 2 rounds.
Baseball and Football rosters are much bigger because there are more positions to play and they have much larger drafts accordingly. Baseball has 3 levels of minor league training, and NFL teams have practice squads, as well as Arena and Canadian leagues as alternatives to the NFL.
This post was edited by Terps on Jun 19 2013 12:54pm