Out of bounds, in baseball (4)
I believe the answer is:
foul
'out of bounds in baseball' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for foul that I've seen before include "Break the rules on the pitch" , "Unfair tackle" , "Revolting" , "Offensive, abominable" , "Obnoxious" .)