A stun grenade was a hand-thrown weapon utilized by both United Earth Starfleet and MACOs in the 22nd century. Designed with a time-delay setting, stun grenades were capable of incapacitating the enemy without causing permanent physical damage, in much the same way as a phase pistol set to stun.
In 2151, Subcommander T'Pol, first officer of the Enterprise, suggested using stun grenades to forcibly remove the descendants of Human colonists on planet Terra Nova, known as "Novans," from the tunnels which they had established beneath the surface. (ENT episode: "Terra Nova")
The next year, Captain Archer, Commander Tucker, and T'Pol, utilized stun grenades in a raid of Suliban stealth cruiser, during their attempt to obtain evidence that the Suliban Cabal had framed them for the destruction of a colony at Paraagan II. (ENT episode: "Shockwave")
Shortly into their mission in the Delphic Expanse, Enterprise was raided by Osaarian pirates. During their attempts to subdue the Osaarians, Captain Archer ordered a MACO to utilize a stun grenade to neutralize one of them in the armory, as using their phase weapons in such close proximity to armed photonic torpedoes was too dangerous. The stun grenade proved ineffective, however, as the Osaarian was able to beam away before it went off. Amongst other items stolen by the pirates were two dozen stun grenades. (ENT episode: "Anomaly")
During a Starfleet mutiny in January 2154, a stun grenade was lobbed inside an airlock aboard a crashed Xindi-Insectoid starship by Commander Charles Tucker III. The weapon's detonation rendered two MACO guards unconscious, inside the airlock. (ENT episode: "Hatchery")
Later that year, Major Joss Hayes and a team of MACOs used a stun grenade to incapacitate two Xindi-Reptilians during a boarding mission to a Xindi-Reptilian warship aimed at rescuing Ensign Hoshi Sato, who had been kidnapped by the Reptilians. (ENT episode: "Countdown")
- Although the script of "Countdown" referred to this device as a "grenade", the script also stated, "This was clearly not a stun grenade."
MACOs still used stun grenades in the 24th century. (Star Trek: Intrepid)