Obstruction bid — a racer confused (9)
I believe the answer is:
barricade
'obstruction' is the definition.
(I know that barricade is a type of boom barrier)
'bid a racer confused' is the wordplay.
'confused' indicates anagramming the letters.
'bid'+'a'+'racer'='bidaracer'
'bidaracer' anagrammed gives 'BARRICADE'.
(Other definitions for barricade that I've seen before include "Obstacle" , "Barrier, to block a street perhaps" , "close up" , "Wall" , "Improvised obstruction" .)