Leading player backing rodents (4)
I believe the answer is:
rats
'rodents' is the definition.
(rat is a kind of rodent)
'leading player backing' is the wordplay.
'leading player' becomes 'star' (I've seen this in another clue).
'backing' says the letters should be written backwards.
'star' in reverse letter order is 'RATS'.
(Other definitions for rats that I've seen before include "Blast" , "(Hunts) rodents - expression of irritation" , "deserters" , "were piped away" , "Damn" .)