Disgusting offence on pitch (4)
I believe the answer is:
foul
'disgusting' is the definition.
(both can mean horrible)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for foul that I've seen before include "Putrid" , "Offensive; make dirty" , "Very unpleasant" , "Having offensive smell or taste" , "Illegitimate tackle" .)