Take clothes off before beginning to enter bar (6)
I believe the answer is:
stripe
'bar' is the definition.
(I've seen this before)
'take clothes off before beginning to enter' is the wordplay.
'take clothes off' becomes 'strip' (I've seen this before).
'before' means one lot of letters go next to another.
'beginning to' indicates taking the first letters.
The initial letter of 'enter' is 'e'.
'strip'+'e'='STRIPE'
(Other definitions for stripe that I've seen before include "Braid showing military rank" , "promotion, maybe" , "Long band of a different colour" , "Sign of a soldier's rank" , "Military rank indicator" .)