Shy drunkard comes back with son (4)
I believe the answer is:
toss
'shy' is the definition.
(both can mean to throw something)
'drunkard comes back with son' is the wordplay.
'drunkard' becomes 'sot' ('sot' can be a synonym of 'drunkard').
'comes back' shows that the letters should be reversed in order.
'with' says to put letters next to each other.
'son' becomes 's'.
'sot' written backwards gives 'tos'.
'tos'+'s'='TOSS'
(Other definitions for toss that I've seen before include "Throw (coin) so as to choose" , "Heads or tails throw" , "Ship's movement" , "What to do with a pancake and a caber" , "Flip; hurl" .)