Topless crowd reportedly witnessed foul (7)
I believe the answer is:
obscene
'foul' is the definition.
(thesaurus)
'topless crowd reportedly witnessed' is the wordplay.
'topless' means to remove the first letter.
'crowd' becomes 'mob' (mob can mean a crowd of people).
'reportedly' shows a homophone (sound like).
'witnessed' becomes 'seen' (similar in meaning).
'seen' is a homophone of 'scene'.
'mob' with its first letter removed is 'ob'.
'ob'+'scene'='OBSCENE'
(Other definitions for obscene that I've seen before include "off colour?" , "Repugnant; indecent" , "Disgusting, repugnant" , "Lewd or loathsome" , "Pseudonym" .)