Common little man seen in bar (9)
I believe the answer is:
prevalent
'common' is the definition.
(prevalent can mean common or widespread)
'little man seen in bar' is the wordplay.
'little man' becomes 'Al' (short for Alex, Alastair etc).
'seen in' indicates putting letters inside.
'bar' becomes 'prevent' (I've seen this before).
'al' put within 'prevent' is 'PREVALENT'.
(Other definitions for prevalent that I've seen before include "Commonplace" , "Ruling" , "general" , "Widespread - current" , "Common" .)