Questioning rioter atoning after conversion (13)
I believe the answer is:
interrogation
'questioning' is the definition.
(interrogation is a kind of questioning)
'rioter atoning after conversion' is the wordplay.
'after conversion' is an anagram indicator (I've seen this in other clues).
'rioter'+'atoning'='rioteratoning'
'rioteratoning' anagrammed gives 'INTERROGATION'.
(Other definitions for interrogation that I've seen before include "Cross-examination" , "Extensive questioning" , "The third degree" , "Systematic questioning" , "Grilling" .)