It is a pretty new gamemode on a game called "Garry's mod" designed by Garry Newman. Basically, it is based on Half Life 2, where the Combine ruled the city. The city was filled with civil protection that protected society from citizen. Which meaning, they beat people and kill people for..... fun.
If your a citizen in HL2RP, you will feel the urge to go "FUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU" on the out of character chatbox.