Their head slides under your reticle
Light leaves your screen and hits your retina. Nothing you own can act yet. One dirty secret before we even start: everything between the server and this moment (their ping, your ping, your display) already delayed this frame. If your TV adds 80 ms of processing, the enemy has been standing there for 80 ms you never got to see. Your display lag steals from a budget you spend in the next step.
peeker's advantage
The player who moves around the corner sees you before you see them, because their movement takes a full network round trip to reach your screen. Attacking beats holding an angle in almost every online shooter for exactly this reason.
Your brain sees, decides, and squeezes
Retina to visual cortex to decision to motor cortex to finger muscle. This is simple reaction time, and it is the single largest number in the entire loop. World class competitors live near 120 ms. Most humans live between 200 and 280. No purchase moves this number; only youth, sleep, caffeine timing, and thousands of hours of training do.
Trigger press travels to the console
Your controller samples the trigger and radios it over. Official first party wireless protocols are fast. Generic Bluetooth pads are two to three times slower. A cable is near instant. This is the cheapest real millisecond purchase on the board, and it is still small.
polling rate
How many times per second the controller reports its state. 125 Hz means up to 8 ms of waiting; 1000 Hz means 1 ms. Esports mice poll at 1000+ for this reason.
The game fires the shot
Your input waits for the next engine tick, the simulation fires the weapon, and the fire packet is built. Sniper rifles in most shooters are hitscan: the bullet is a ray with no travel time. The stages here quantize to frame boundaries, which is why 120 fps genuinely helps: every queue in the pipeline gets cut roughly in half.
hitscan vs projectile
Hitscan weapons (most rifles, snipers) resolve instantly along a ray. Projectile weapons (rockets, arrows) simulate travel time and need you to lead the target.
The packet sprints to the server
Half of your ping. Fiber moves your kill at two thirds the speed of light. WiFi does not make this much longer on average; what WiFi adds is jitter, the random spikes, and the netcode buffers to your worst moments, not your average. A steady 40 ms connection beats a spiky 20.
ping / RTT
Round trip time for a packet to reach the server and come back. One way is roughly half. Under 40 ms round trip is good for shooters.
jitter
The variance in your ping. The silent killer. Games buffer input to survive your spikes, so high jitter quietly adds latency even when average ping looks great.
The server declares them dead
This is where the kill actually happens. The server rewinds the world to exactly what your screen showed when you clicked, checks the ray against their head hitbox, zeroes their health, and writes the kill to the match. Score, K/D, the killfeed: all settled here, roughly a quarter second after the frame that started your squeeze. The other player is now dead in every way that counts. They do not know it yet.
lag compensation
The server trusts the shooter's view of the world at trigger time. It is why you sometimes die after reaching cover: on the shooter's screen, you never made it.
tick rate
How many times per second the server updates the world. 60 Hz means the server thinks in 16.7 ms steps. Higher tick servers settle fights with finer time resolution.
The bad news rides to their console
Half of the victim's ping. During this entire southbound trip, and for a while after, they are still playing. Strafing. Maybe lining up their own shot on you. Fully alive on their own screen, in a present the server has already overruled.
Their body drops on their display
Their console applies the death on its next tick, renders the ragdoll, and their display draws it (their TV's game mode matters here exactly like yours does). Fun symmetry: your skull medal and their death animation land at nearly the same wall clock instant, about 50 ms after the server's verdict.
"Dang, dude. He shot me."
Photons from their own death reach their retina, and their nervous system needs about 100 ms to detect that something happened and another couple hundred to comprehend it: sniper, that ridge, dead. Their conscious experience of your shot arrives a third of a second after the server logged it, and roughly half a second after the frame where you started squeezing.
The full loop, human to human, is a third to half a second. And most of it is meat, not machine.