Miss crossing familiar sea for first prize (4,5)
I believe the answer is:
gold medal
'first prize' is the definition.
(eg at the Olympics)
'miss crossing familiar sea' is the wordplay.
'miss' becomes 'gal' (synonyms).
'crossing' is an insertion indicator.
'familiar' becomes 'old' (old can mean familiar or traditional).
'sea' becomes 'med' (short for Mediterranean).
'old'+'med'='oldmed'
'gal' enclosing 'oldmed' is 'GOLD MEDAL'.
'for' is the link.
(Other definitions for gold medal that I've seen before include "Award for Olympic winner" , "prize for winning" , "Possible alternative to cup" , "top award" , "First prize" .)