Versus mode is 2-player co-op on the same console. Turn on a 2nd controller and choose sides. Once the game begins you can make player 2 forfeit, giving you a win. Repeat that 4 times. Alternately, you can play through it. It's quicker to use the zombies. Spawn the regular zombie and send him down a lane without any pea-shooters. Once he breaks through the defense the lawn mower will kill him. After the lawn mower is gone, spawn a football player and send him down the same lane. He will run all the way down and enter the house, you win! Repeat 4 more times for this easy achievement.