Superhero arrests small player (7)
I believe the answer is:
batsman
'player' is the definition.
(I know that batsman is a type of baseball player)
'superhero arrests small' is the wordplay.
'superhero' becomes 'Batman' (DC superhero).
'arrests' is an insertion indicator (inserted letters are held or arrested).
'small' becomes 's' (abbreviation - e.g. clothes size).
'batman' enclosing 's' is 'BATSMAN'.
(Other definitions for batsman that I've seen before include "Hitting ballplayer" , "Cricketer at the crease" , "He's either in or he's out!" , "one of two on the field" , "One at the crease" .)