Reassemble after a defeat (7)
I believe the answer is:
regroup
'reassemble after a defeat' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for regroup that I've seen before include "Reassemble after a defeat" , "Assemble after defeat" , "Gather (after an attack)" , "form new parties" , "make new arrangements" .)