What you need to be a...
Pitcher - endurance, stamina, strong nerves, ability to throw across the plate, control
Catcher - tough, quick reflexes, no fear, strong arm, ability to throw to second base
First Baseman - agile, ability to set a good target
Second Baseman - quick, ability to avoid base runners, good range, good fielding skills
Third Baseman - good reflexes, ability to throw to first base, no fear of the ball
Shortstop - quick, good range, ability to throw to first, ability to lead the infield
Right Fielder - strond arm, good perception, ability to stay focused
Left Fielder - strong arm, good perception, ability to stay focused
Center Fielder - strong arm, good perception, ability to stay focused, quick, ability to lead the outfield