"The Resolve system protects individual players from having their character repeatedly controlled by enemy players inside Player vs Player combat. Each character possesses a Resolve resource bar, visible above the character in his or her nameplate, next to the portrait on the targeting window, and in the group window. When a character is the target of an enemy stun, sleep, knockdown, blind, or ballistic effect, that character gains an amount of resolve points. This value is based on the type of effect and its duration, with stronger effects like stun and knockdown generating more resolve than weaker effects like sleeps and blinds. Additionally, if there are control effects currently active on the target, subsequent control effects add a smaller amount of resolve based on the strength and remaining duration of those effects. Gaining resolve points fills up the character’s resolve with a purple bar. Once the resolve bar fills completely up the bar turns white and the character becomes immune to further control effects. When all current control effects expire the resolve bar begins to decay to zero resolve, at which point the character once again can be controlled and the building process starts anew."
―In-game Codex (Game Rules)[src]

As soon as you get flagged for pvp you will get a resolve bar next to your portrait. This bar fills up when you are affected by other players crowd control abilities. When the bar gets full you will become immune to further crowd control abilities for a brief time.

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