Concerned with split in stage, not for the first time (5)
I believe the answer is:
rerun
'stage not for the first time' is the definition.
(stage on a further occasion)
'concerned with split' is the wordplay.
'concerned with' becomes 're' (re can mean regarding, concerning).
'split' becomes 'run' (split can mean to run away).
're'+'run'='RERUN'
'in' is the link.
(Other definitions for rerun that I've seen before include "Repeat of event" , "Broadcast or print again" , "rush again" , "Performed or broadcast again" , "return to track" .)