"Know it all' Paul to the rescue.
Oversimplified and kinda inaccurate. Realistically, you'd be using all of the lobes for each of those described tasks. For instance: To perceive and react to an enemy player, your eyes would receive the light rays from the computer screen, which would then be transmitted to and processed by the occipital lobe. And subsequently, your parietal lobe would be determining the dimensions and location of the enemy, relative to other objects. Meanwhile your temporal lobe would be assigning the verbal label of "enemy" to the well, enemy, and combining relevant sounds to the visual information associated with the "enemy" (e.g. footsteps, gunshot noises). And your frontal lobe would be deciding where to shoot the "enemy", and assigning other relevant judgements to the situation (such as "start/stop shooting", "burst or spray"). Also, your frontal lobe would be controlling the manual movement of the muscles in your arm as you control the mouse/keyboard, and your cerebellum would help with coordinating those physical movements.