In the act (3-6)
I believe the answer is:
red-handed
'in the act' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for red-handed that I've seen before include "(Caught) in the act of committing a crime" , "(Taken) in the act" , "Caught ... ......, apprehended in the act of crime" , "In the act of crime - may be caught thus" , "Catch someone thus in the act" .)