Whip's firm push on Reeves's back (7)
I believe the answer is:
scourge
'whip's' is the definition.
(scourging is a kind of whipping)
'firm push on reeves's back' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'push' becomes 'urge' (I've seen this in another clue).
'on' is a charade indicator (letters next to each other).
'back' indicates one should take the final letters (the letter at the back).
The final letter of 'reeves' is 's'.
'co'+'urge'='courge'
'courge' after 's' is 'SCOURGE'.
(Other definitions for scourge that I've seen before include "Whip used to inflict punishment" , "Bane, curse" , "source of evil" , "One providing lashings" , "big nuisance" .)