Obstacle in the pub (3)
I believe the answer is:
bar
I believe this clue is a double definition.
'obstacle' is the first definition.
(bar can mean an obstacle or blockage)
'pub' is the second definition.
(both are drinking establishments)
'in the' acts as a link.
(Other definitions for bar that I've seen before include "Save; pub" , "Impediment" , "Watering hole" , "whose moaning Tennyson hoped to prevent?" , "Pub; ban" .)