During which event are participants required to throw a grenade?

The grenade throw is a specific component of the Marine Corps Combat Fitness Test that takes place during the ammo run event. This part of the test evaluates a Marine's ability to handle the physical demands of carrying ammunition while also demonstrating the skill necessary to accurately throw a grenade. The ammo run requires participants to carry a weighted box, simulating the transport of ammunition, and includes the grenade throw as a critical skill requirement that reflects combat readiness. This emphasis on throwing a grenade, alongside physical endurance and strength, highlights the dual aspects of combat training, combining practical skills with overall fitness. Other events listed, such as the 300-yard shuttle run, buddy carry, and fireman carry, while important for assessing different physical capabilities, do not involve the grenade throw component, making the ammo run the correct answer in this context.