Derek Slater's new hat (11)
I believe the answer is:
deerstalker
'hat' is the definition.
(deerstalker is a kind of hat)
'derek slater's new' is the wordplay.
'new' is an anagram indicator.
'derek'+'slater'='derekslater'
'derekslater' with letters rearranged gives 'DEERSTALKER'.
(Other definitions for deerstalker that I've seen before include "Soft cloth hat" , "Type of cloth cap" , "Hunter - hat" , "it goes to one's head" , "Hunting cap" .)