Meaning of “foul” - Learner’s Dictionary

foul

verb uk us /faʊl/
DIRTY [ T ]

to make something very dirty:

The beaches had been fouled by dogs.
SPORT [ I, T ]

to do something that is against the rules in a sport:

He was fouled as he was about to shoot at goal.

(Definition of “foul verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)