Lob some balls, so thrown back (4)
I believe the answer is:
toss
'lob' is the definition.
(I've seen this before)
'some balls so thrown back' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'back' shows that the letters should be reversed in order.
'ssot' is hidden within 'balls so thrown'.
'ssot' reversed gives 'TOSS'.
(Other definitions for toss that I've seen before include "decision-making process" , "Throw into the air" , "Careless not to give this" , "Raise a bit of money before opening" , "ball" .)