Behold 150 gathered round a pub (5)
I believe the answer is:
local
'pub' is the definition.
(one's local pub)
'behold 150 gathered round a' is the wordplay.
'behold' becomes 'lo' ('lo' is an archaic exclamation meaning 'look!').
'150' becomes 'CL' (roman numerals).
'gathered round' indicates putting letters inside.
'cl' going around 'a' is 'cal'.
'lo'+'cal'='LOCAL'
(Other definitions for local that I've seen before include "Belonging to a particular place" , "stopping train" , "belonging to particular area?" , "round the corner" , "Pub around the corner?" .)