Flare

From MLGWiki

The Flare is a piece of equipment which blinds any players who are within a certain range of it until it deactivates after five seconds. The closer a player is to it, the greater the blinding effect. The flare is effective for breaking up engagements or blinding snipers as players move in.

Players blinded by the Flare can still see their HUD, however, so it is possible to shoot at enemies by watching for the reticule to turn red.