Clean off a spear (5)
I believe the answer is:
lance
'a spear' is the definition.
(I know that spear can be written as lance)
'clean off' is the wordplay.
'off' indicates an anagram.
'clean' with letters rearranged gives 'LANCE'.
(Other definitions for lance that I've seen before include "corporal may have at the front" , "Long pointed weapon of old" , "Shafted weapon used on horseback" , "Knightly weapon" , "Long, pointed weapon (5)." .)