Trendy bishop booted out of seaside town (5,2)
I believe the answer is:
right on
'trendy' is the definition.
(both can mean fashionably progressive)
'bishop booted out of seaside town' is the wordplay.
'bishop' becomes 'B' (abbreviation for bishop in chess).
'booted out of' suggests deleting specific letters.
'seaside town' becomes 'Brighton' (Brighton is by the sea).
'brighton' with 'b' removed is 'RIGHT-ON'.
(Other definitions for right on that I've seen before include "Very PC - exclamation of agreement" , "PC, perhaps" , "Words of encouragement" , "Trendy and socially aware" , "Absolutely!" .)