Win back concerning company before period of success (6)
I believe the answer is:
recoup
'win back' is the definition.
(I've seen this before)
'concerning company before period of success' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'company' becomes 'co' (abbreviation).
'before' says to put letters next to each other.
'period of success' becomes 'up' (as in ups and downs).
're'+'co'+'up'='RECOUP'
(Other definitions for recoup that I've seen before include "Regain (something lost)" , "Recover - retrieve" , "Indemnify" , "Win back" , "make good one's losses" .)