Goalkeepers tend to get a hard time of it, especially when they've got opposition supporters behind the goal trying to put them off at every opportunity. From laser pointers to good old fashioned abuse, there's various ways to get into a goalkeepers head. Gremio fans might have taken it a step too far though.
During a recent league match fans of Gremio thought the best way to put the opposing goalkeeper off was by firing fireworks directly at him. The other team actually went on to score, but the referee disallowed the goal after clearly noticing the goalkeeper was horrifically put off. Allowing it to stand might have served those brainless Gremio fans right, though.