Finish first in stage, leading (4)
I believe the answer is:
stop
'finish' is the definition.
(I know that finish can be written as stop)
'first in stage leading' is the wordplay.
'first in stage' becomes 's' (1st letter of 'stage').
'leading' becomes 'top' (both can mean first-class).
's'+'top'='STOP'
(Other definitions for stop that I've seen before include "Check" , "Knock out" , "port of call" , "Come to a halt" , "Withhold large amount raised" .)