Knight game (5)
I believe the answer is:
joust
'knight game' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for joust that I've seen before include "Participate in tournament" , "Tilt - tourney" , "Engage in knightly tournament" , "Contest for mounted knights" , "Fight on horseback like a knight" .)