Rooting Section
Cheer Squad, Cheering Section
noun
A group that roots for you is your rooting section or cheer squad. Go go go you!
応援団 tend to wear black school uniforms and support their team with lively chants and energetic performances. They can also have cheerleaders with pom-poms, but those are usually just called チアリーダー.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. 応援 is a word you've seen before, so if you know that this word will be easier.
中学校の時は野球部の応援団の一員でした。
When I was in middle school I was a member of the cheering section for the baseball club.
コウイチは、トーフグ応援団について聞かれても、肩をすくめるだけだった。
Koichi just shrugged his shoulders when asked about the Tofugu rooting section.
ああ、君が応援団長だね？噂はかねがね伺っておるよ。
Hey, you're the leader of the cheer squad, right? I’ve heard a lot about you.