Antagonize (4)
I believe the answer is:
rile
'antagonize' is the definition.
(I know that antagonize is a more specific form of the action rile)
This is all the clue.
(Other definitions for rile that I've seen before include "Get up nose of" , "Informally, annoy or irritate" , "Irritate considerably" , "bug" , "Annoy, nettle" .)