Exposed a redhead in the sack (5)
I believe the answer is:
bared
'exposed' is the definition.
(baring is a kind of exposing)
'a redhead in the sack' is the wordplay.
'redhead' becomes 'r' (the head/first letter of 'red').
'in the' indicates putting letters inside.
'sack' becomes 'bed' ('in the sack' means 'in bed').
'a'+'r'='ar'
'ar' inserted into 'bed' is 'BARED'.
(Other definitions for bared that I've seen before include "Uncovered" , "Stripped" .)