Clarets, perhaps, or their Premiership rivals? (4)
I believe the answer is:
reds
'clarets perhaps' is the definition.
(claret is a kind of red)
I don't understand how the remainder of the clue works.
(Other definitions for reds that I've seen before include "Scarlet and crimson, say" , "Colourful communists" , "Scarlet communists" , "Colours for communists" , "First snooker balls to be potted" .)