A Shield is a power-up available in Blast Ball in Metroid Prime: Federation Force. It is collected by shooting the ball repeatedly and picking up the item. When used, a red barrier forms around the contestant, which temporarily renders them invincible and causes severe damage to anyone who comes into contact with it. It is the only way that contestants can avoid ejection from their Mechs if the opposite team uses the Eject item.
"Shields a player from damage. It will also prevent the player from being affected by the Eject item."