Swaggering (5)
I believe the answer is:
cocky
'swaggering' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cocky that I've seen before include "Remove errors from (program)" , "Boldly conceited" , "Cheekily conceited" , "Boldly self-confident" , "Cheeky and self-confident" .)