Cut a line that's bitten by sea cat (9)
I believe the answer is:
medallion
'cut' is the definition.
(I've seen this before)
'a line that's bitten by sea cat' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'that's bitten by' is an insertion indicator (I've seen this in other clues).
'sea' becomes 'med' (short for Mediterranean).
'cat' becomes 'lion' (lion is a kind of cat).
'a'+'l'='al'
'med'+'lion'='medlion'
'al' placed within 'medlion' is 'MEDALLION'.
(Other definitions for medallion that I've seen before include "Ornamental disc on a chain" , "Mad O'Neill wins the award" , "Circular decorative device - model nail (anag)" , "Cut" , "Circular piece of meat - commemorative award" .)