The weeklong game, played at over 650 universities, begins with an approximately 1:30 zombie:human ratio, and ends with a final mission. Zombies wear orange bandannas around their heads; humans, around their bulging biceps. Stunned zombies wear bandannas around their necks for ten minutes, during which they walk in shame. A zombie may "turn" a human by eating its brains out, literally.
Well, by tagging a human with its hand, a zombie may figuratively eat the human's brains, thus turning it into a zombie(after a ten-minute transformation period).
A human may stun a zombie for ten minutes by hitting it with a thrown sock or(with higher success rates)shooting it with a Nerf blaster. I myself have shot many a zombie with my trusty Maverick.
Achievements may be earned for such feats as surviving a certain number of days as a human, a day in costume, tagging a certain number of humans, tags while wearing a costume, or a lot of other cool things. Man there are some really cool things that you can do. There are over 20 achievements, depending on what school you're playing at. My personal favorite is the ZOMGWTF achievement; as a human, you hit a live zombie with a thrown Nerf dart and live to tell the tale.
HvZ has many more details and stipulations; take a look at their website if you're intrigued :)
All players begin as humans and wear a bandana on their arm. A player is chosen by the moderators to be the original zombie (OZ). Zombies usually move their arm bands to their heads, to show that they've turned, but depending on the game, the OZ can stay anonymous for a day, or until a certain killcount.
The OZ tags as many humans as possible, turning them into zombies. Each zombie must tag a human every 2 days, or the zombie starves, and is out.
Mods monitor zombie kills and human transformations using an online program. All players are given an alphanumerical code before gameplay begins. When a zombie tags a human, the human must give the zombie their code. The zombie enters the code into the computer program. This process monitors the times that a zombie has fed, as well as what humans have been eaten.
Humans defend themselves from zombies by shooting nerf guns or throwing socks. If hit, the zombie is stunned for 15 min.
Safe zones are areas where zombies can't attack humans. Depending on the game, offcampus areas can also be considered safe zones.
Missions are created by mods to keep humans from hiding all game.
Guy 2: Don't you know, man? There's a humans vs zombies game this week. The zombie apocalypse is upon us!
Guy 1: Aww man, I missed the sign up. Gonna need to do that next time, by going to www.humansvszombies.org.
This is what people do in college who don't drink, dance, work or do anything a normal person would consider socially acceptable.
The death of a college campus for a week.
Person 2: It's humans vs zombies.
Person 1: Damnit, I hate nerds.