Beat young farm animal endlessly (3)
I believe the answer is:
lam
'beat' is the definition.
(I know that lam is a more specific form of the action beat)
'young farm animal endlessly' is the wordplay.
'young farm animal' becomes 'lamb' (young sheep).
'endlessly' means to remove the last letter.
'lamb' with its last letter taken off is 'LAM'.
(Other definitions for lam that I've seen before include "Flee hastily" , "Beat hard" , "On this, you're in flight, especially from the police" , "On this, you're fleeing, from the police" , "Batter" .)