The Thunderstick is an offensive weapon used by S.H.I.E.L.D. agents that releases a wave of sonic energy designed to quickly incapacitate an attacking force.
The weapon releases an explosive-device to launch the sonic wave, and has a spiked end to easily secure it in the ground.
During the investigation of an 0-8-4 in Peru, Coulson's Team was attacked by Peruvian rebels. Agent Grant Ward used the Thunderstick to incapacitate a large amount of enemies surrounding the team.
During the HYDRA Uprising, in the Battle at the Hub, following the revelation that John Garrett was the mysterious "Clairvoyant" and an agent of HYDRA, Garrett and Agent Phil Coulson were locked in combat when Leo Fitz tossed him a Thunderstick which Coulson used to defeat Garrett.
According to the technical report, it was the size of a police baton. It also emits a powerful 360-degree shock wave capable of incapacitating any biological life-form within range.