"The Siege Mode is a six-player affair that pits players against each other in 3-on-3 bouts, with three players taking on the role of zombies and three players taking on the role of BSAA members. The objective is for the BSAA members to protect the rookies while the zombies have to kill the rookies. If the BSAA can hold out until time expires, they win. If the zombies can kill the rookies before time expires, they win. Check it out in the new promo trailer."