Possesses under 150 buffoons (6)
I believe the answer is:
clowns
'buffoons' is the definition.
('clown' can be a synonym of 'buffoon')
'possesses under 150' is the wordplay.
'possesses' becomes 'owns' ('own' can be a synonym of 'possess').
'under' says to put letters next to each other (in a down clue, some letters go below others).
'150' becomes 'CL' (Roman numerals).
'owns' after 'cl' is 'CLOWNS'.
(Other definitions for clowns that I've seen before include "idiotic people" , "Funny men in the circus" , "Circus entertainers" , "They amuse with ridiculous behaviour" , "Funny circus folk" .)