Screaming or shouting during the moment of watching games can't be taking away from the game because doing so is going to kill the excitement that the game is renowned for. Historically, this act of screaming can be dated back to ancient times when the gladiators were doing battles in the arena. Back then, the crowd specting the fighters often come alive when their favorite fighters are gaining upper hand in the battle.
Fast forward to this present day games, fans are also taking cue from what was applicable then in the erena, that's why they would be screaming on top of their voice to express their support for their various teams. The fans are so passionate about the game been played that all they can do to go with the thrill and frill is by letting out their inner excitement through screaming, especially if their teams are on the wining side.