Believe me. . . They Aren't Injured, Just Teenage Guys.
It may have been a very difficult era for these young teenage boys, but who's to stop them from wrecking mass havoc with each other (Remind you of a certain group of guys in this school? [No Offense Intended in this Blog Post!]).
Grenades may have been around since the time of the Byzantine Empire or Song Dynasty, but none of those "primitive" grenades could compare to the evolution of the hand grenade during World War I.