Lethal striker clubs old supporter (5)
I believe the answer is:
cobra
'lethal striker' is the definition.
'clubs old supporter' is the wordplay.
'clubs' becomes 'c' (abbreviation used in card games such as bridge).
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'supporter' becomes 'bra' (a bra gives support to breasts).
'c'+'o'+'bra'='COBRA'
(Other definitions for cobra that I've seen before include "crisis response group" , "Something with a hood" , "Highly venomous hooded reptile" , "Reptile (found in Cabinet Office Briefing Room A?)" , "Venomous Asiatic and African elapid snake" .)