Gem of a wicket (5)
I believe the answer is:
agate
'gem' is the definition.
(agate is a kind of gem)
'a wicket' is the wordplay.
'wicket' becomes 'gate'.
'a'+'gate'='AGATE'
'of' is the link.
(Other definitions for agate that I've seen before include "Ornamental form of quartz" , "Stone with coloured bands" , "Variegated chalcedony" , "Precious stone" , "rock with bands" .)