Flashbang

The M84 stun grenade is the flashbang used in Call of Duty 4: Modern Warfare. A flashbang is a grenade that releases a flash of light that momentarily activates all photosensitive cells in the retina, making vision impossible for approximately five seconds until the eye restores the retina to its original, unstimulated state. Subjects affected by flashbangs describe seeing a single frame for the five seconds (as if their vision was "paused") until it fades and normal sight returns. This is because the sensory cells which have been activated continue sending the same information to the brain until they are restored to their resting state, and the brain translates this continuous information into the same image. The incredibly loud blast emitted by the grenade contributes to its incapacitative properties by disturbing the fluid in the semicircular canals of the ear. In Call of Duty, the flash bang has a much larger radius than the stun grenade.

Tactics
The Flash grenade can be effectively used on a defended location or around a corner. If the target is close enough and looking at the detonation site, they will be temporarily blinded and deafened. The target’s reaction is still in real time so they can run or back-up to evade, however, they cannot sprint while affected. They can still easily fire, making any enemy in front of them a potential kill. Any affected target will raise their arm to cover their eyes, allowing the player to know that they are blinded. This weapon will also affect teammates and the player throwing it.

In the single-player game, you spawn with and can find flash grenades in grenade bags, but they only show up in bags when you don't have a lot of them. In multiplayer, if you go into last stand while cooking a flashbang it will turn into a frag grenade. Flash Grenades will go off in the air. They will not wait until they hit the ground like stun grenades, so don't chuck them straight up.