Standard title for men now acting upset (4)
I believe the answer is:
norm
'standard' is the definition.
(I know that standard can be written as norm)
'title for men now acting upset' is the wordplay.
'title for men' becomes 'Mr' (title given to men).
'now acting' becomes 'on' (on stage).
'upset' says the letters should be written in reverse.
'mr'+'on'='mron'
'mron' in reverse letter order is 'NORM'.
(Other definitions for norm that I've seen before include "(The) accepted way" , "Benchmark" , "Accepted standard of behaviour" , "Standard amount or customary behaviour" , "Something typical" .)