Fury over Rex playing a stage villain (6)
I believe the answer is:
virago
'fury' is the definition.
(thesaurus)
'over rex playing a stage villain' is the wordplay.
'over' indicates putting letters inside.
'rex' becomes 'R' (common abbreviation e.g. GR=George Rex, King Georg).
'playing' becomes 'v' ('playing' can mean 'versus' in sports).
'a stage villain' becomes 'iago' (I've seen this before).
'v'+'iago'='viago'
'r' going within 'viago' is 'VIRAGO'.
(Other definitions for virago that I've seen before include "Harridan" , "Bad-tempered woman" , "Shrew - ill-tempered woman" , "Strong and aggressive woman" , "Loudly fierce or abusive woman" .)