Unexpectedly jeers youth leader in Channel Island (6)
I believe the answer is:
jersey
'channel island' is the definition.
(I've seen this before)
'unexpectedly jeers youth leader' is the wordplay.
'unexpectedly' indicates an anagram.
'youth leader' becomes 'y' (I've seen this in other clues).
'jeers' with letters rearranged gives 'jerse'.
'jerse'+'y'='JERSEY'
'in' is the link.
(Other definitions for jersey that I've seen before include "CI; cow" , "One over the moon might have been such" , "One of the Channel Islands" , "Top - cow" , "Warm garment or Channel Island" .)