1. Throw quick punches on the ground, dash back after landing 3-4 hits to avoid his counter attack.
2. Shoot from distance.
3. Climb walls (and jump over) when he shoots from bottom to top.
4. Jump down and crouch when he shoots from top to bottom.
5. Punch his grenade back on him (needs to be still in the air?).
6. ???
8. Profit!