Get back together on set (7)
I believe the answer is:
regroup
'get back together' is the definition.
(I've seen this before)
'on set' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'set' becomes 'group' (group is a kind of set).
're'+'group'='REGROUP'
(Other definitions for regroup that I've seen before include "make new arrangements" , "Assemble after defeat" , "Gather (after an attack)" , "Rally" , "Organise again after a defeat" .)