Silly sports coats and old hat (5)
I believe the answer is:
passe
'old hat' is the definition.
(old hat can mean passe or outdated)
'silly sports coats' is the wordplay.
'silly' becomes 'ass'.
'sports' becomes 'pe' (Physical Education).
'coats' is an insertion indicator (inserted letters are coated in another word).
'ass' put within 'pe' is 'PASSE'.
'and' is the link.
(Other definitions for passe that I've seen before include "Outdated" , "Past its prime - in France" , "dated" , "Old fashioned - in France" , "-- -partout" .)