Back stage for this hair preparation (3)
I believe the answer is:
gel
'this hair preparation' is the definition.
(I've seen this before)
'back stage' is the wordplay.
'back' is a reversal indicator.
'stage' becomes 'leg' (a leg is a stage of a competition).
'leg' back-to-front is 'GEL'.
'for' acts as a link.
(Other definitions for gel that I've seen before include "well-spoken deb?" , "Jelly-like substance for leg" , "It may be applied to locks" , "Work well together" , "Hair treatment" .)