Give refill to young boxer, perhaps (3,2)
I believe the answer is:
top up
'give refill' is the definition.
'to young boxer perhaps' is the wordplay.
I cannot really see how this works, but
'to' is present in the answer.
'young' could be 'pup' (pup is a kind of young) and 'pup' is located in the answer.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for top up that I've seen before include "Replenishment of drink" , "Addition restoring former level" , "Replenish" , "Add a little reason" , "Amount required to restore something's level" .)