Pike thrown into head wear (4)
I believe the answer is:
kepi
'head wear' is the definition.
'kepi' can be an answer for 'wear' (kepi is a kind of wear). I'm not certain of the 'head' bit.
'pike thrown' is the wordplay.
'thrown' indicates an anagram.
'pike' anagrammed gives 'KEPI'.
'into' is the link.
Can you help me to learn more?
(Other definitions for kepi that I've seen before include "French army cap" , "Service cap" , "French military hat" , "French military cap" , "French military headgear" .)