Perfectly acceptable penalty (4)
I believe the answer is:
fine
I believe this clue is a double definition.
'perfectly acceptable' is the first definition.
(fine can mean satisfactory)
'penalty' is the second definition.
(fine is a kind of penalty)
(Other definitions for fine that I've seen before include "musical ending" , "French brandy" , "Sheer or excellent" , "Monetary penalty - that's splendid" , "No special brandy" .)