Hit Judy's companion (5)
I believe the answer is:
punch
'hit' is the definition.
(I know that punch is a more specific form of the action hit)
'judy's companion' is the wordplay.
'judy' becomes 'pun' (I can't explain this - if you can you should give a lot more credence to this answer).
'companion' becomes 'ch' (Companion of Honour).
'pun'+'ch'='PUNCH'
Can you help me to learn more?
(Other definitions for punch that I've seen before include "Tool for making a hole" , "Hit with a fist" , "Strike, Judy's husband" , "that would be attached to haywain for pulling?" , "horse to get > drink" .)