Guard mounting is when someone sits on top of another person's hips and legs to control and immobilize them. It's like when you sit on your friend's belly during playtime, but instead of just playing, the person on top is trying to keep the person underneath from moving or getting up. It's an important move in martial arts and self-defense because it allows the person on top to control the other person and possibly get them to give up or submit. But it's also important to remember to only use force when necessary and not to hurt anyone.