It works like this:

You defend against the attack from the poster above you and then you attack the poster below you.


Example:

Quote:
Poster #1

Attack: *Throws rock at next poster*


Quote:
Poster #2

Defend: *Holds up garbage can lid to deflect the rock*

Attack: *Throws flaming wad of paper at next poster*


I'll start:

Attack: *Throws banana flambe at next poster*