Come together on returning (3)
I believe the answer is:
gel
'come together' is the definition.
(I've seen this before)
'on returning' is the wordplay.
'on' becomes 'leg' (cricket term, fielding positions).
'returning' is a reversal indicator.
'leg' reversed gives 'GEL'.
(Other definitions for gel that I've seen before include "Colloid" , "Begin to work" , "Leg (anag.)" , "Viscid substance" , "Mousse" .)