noun
supporter; cheerer; rooter
A person who supports or cheers for someone or a team, often at sporting events or competitions.
彼は熱心な応援者だ。
He is an enthusiastic supporter.
試合では多くの応援者が声援を送った。
Many cheerers shouted encouragement at the match.
Compound of 応援 (ouen, 'support, cheering') + 者 (sha, 'person').