Equivalent role supporting bar (11)
I believe the answer is:
counterpart
'equivalent' is the definition.
(counterpart is a kind of equivalent)
'role supporting bar' is the wordplay.
'role' becomes 'part' ('part' can be a synonym of 'role').
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'bar' becomes 'counter' (I've seen this before**).
'part' after 'counter' is 'COUNTERPART'.
(Other definitions for counterpart that I've seen before include "See opposite number" , "Match" , "Each of two copies of a legal document" , "Duplicate" .)