During the match the cheer squad waved flags and roared from the sidelines.
Tips
history
From the Yuan zaju 《两世姻缘》 by Qiao Mengfu - 你这般摇旗呐喊,簸土扬沙 ('you're there waving flags and shouting, kicking up dust'). Originally the foot-soldier's role in battle: not fighting, but making noise to back up others.
usage
Often slightly deflating when applied to adults - suggests the person isn't the main actor, just a loud supporter. Neutral to positive when applied to fans/cheerleaders.