The deflector plate is an item in Gamer 2. Kora gives it to Hailey at the beginning of the game.
Hailey can survive taking damage from any source while she has the plate, but it will be knocked off and she must retrieve it to regain that security. Hailey can also gain a new plate by touching any checkpoint. While missing her deflector plate, a red exclamation point will flash over Hailey's head.
Kevin has his own deflector plate that behaves similarly when Hailey fights him in the arena level. Unlike Hailey's, his is yellow.