Hands over in exchange (4)
I believe the answer is:
swap
'exchange' is the definition.
(swapping is a kind of exchanging)
'hands over' is the wordplay.
'hands' becomes 'paws' ('paw' can be a synonym of 'hand').
'over' says the letters should be written backwards.
'paws' backwards is 'SWAP'.
'in' acts as a link.
(Other definitions for swap that I've seen before include "Exchange, barter" , "Change over" , "Exchange for paws" , "exchanged gift" , "exchanged item" .)