Occasional visitor glassed? (5,4)
I believe the answer is:
guest beer
'occasional visitor glassed?' is the definition.
I can't judge whether this defines the answer.
'visitor glassed?' is the wordplay.
'visitor' becomes 'guest' (guest is a kind of visitor).
'glassed?' becomes 'beer' (I can't explain this - if you can you should believe this answer much more).
'guest'+'beer'='GUEST BEER'
(Other definitions for guest beer that I've seen before include "Temporarily-available tipple" , "Pub's irregular offering" , "Not a pint of the usual" .)