Measuring latency from stimulus to action
Reaction time in FPS games is not the same as raw cognitive reaction speed. A professional CS or Valorant player with a 200ms reaction time is responding not to a visual stimulus in isolation, but to a complex read of the game state. They see an opponent pre-aim their peek angle, recognize the threat pattern from thousands of hours of similar encounters, and shoot before the opponent's crosshair reaches them. This is part prediction, part execution. A bottom-tier amateur at 320ms is making the same decision but with less pattern recognition, worse aim, and higher input lag.
Why 15-30ms separates skill tiers
In duels that last under 500ms (one shot, one kill), a 100ms reaction gap is insurmountable. Professional players cluster around 150-250ms, while casual players average 300-400ms. The gap is not raw neurological difference; it is a combination of monitor refresh rate (pros use 240Hz, casuals 60Hz), mouse polling rate (8,000Hz vs 125Hz), sensitivity tuning, and tens of thousands of hours of practice that compresses decision time. A casual player with pro-level gear and 1,000 hours of practice can cut 80ms off their reaction time.