Change hands over (4)
I believe the answer is:
swap
'change' is the definition.
(I know that swap is a more specific form of the action change)
'hands over' is the wordplay.
'hands' becomes 'paws' ('paw' can be a synonym of 'hand').
'over' shows that the letters should be reversed in order.
'paws' back-to-front is 'SWAP'.
(Other definitions for swap that I've seen before include "Exchange, barter" , "Substitute' feet backwards" , "Fifty-fifty odds" , "Interchange" , "Exchange for paws" .)