Turn on hair product (3)
I believe the answer is:
gel
'hair product' is the definition.
(hair gel)
'turn on' is the wordplay.
'turn' says the letters should be written backwards.
'on' becomes 'leg' (cricket term, fielding positions).
'leg' back-to-front is 'GEL'.
(Other definitions for gel that I've seen before include "Come together, take shape (colloq.)" , "Hair-dressing preparation" , "stiffen" , "posh lass" , "Substance to fix hair in place" .)