Helmet that protects at the crease (3,3)
I believe the answer is:
tin hat
'helmet' is the definition.
(tin hat is a kind of helmet)
'that protects at the crease' is the wordplay.
'protects' indicates putting letters inside (outer letters protect inside letters).
'at the crease' becomes 'in' (cricket term).
'that' enclosing 'in' is 'TIN HAT'.
(Other definitions for tin hat that I've seen before include "Soldier's helmet" , "Headgear, worn for protection" , "Protective helmet once worn by constuction and mine workers" , "Steel helmet (informal)" , "Finish it off to put the protective headgear on it" .)