Sorry if this is a repost. Never seen this before, and discovered this today. It's pretty fun.
The video is the explanation.
[ame=http://www.youtube.com/watch?v=DPU0_ilKE3U]YouTube - Fiveshot's Forced PvP Flag Trick[/ame]
No i didn't hide my name. Cuz i don't really think i'm breaking any rules. Just a clever little trick