Mark on uniform damaged in riot (3,4)
I believe the answer is:
run amok
'riot' is the definition.
(thesaurus)
'mark on uniform damaged' is the wordplay.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'damaged' is an anagram indicator.
'mark'+'on'+'u'='markonu'
'markonu' anagrammed gives 'RUN AMOK'.
'in' acts as a link.
(Other definitions for run amok that I've seen before include "Rampage" , "Go berserk" , "Go on frenzied, murderous spree" , "go on killing spree" .)