Hiroki Oyama (小山大樹 Oyama Hiroki) is the shortstop and captain of Sakitama High School's baseball team.
He is the only third year on the current baseball team.
Oyama has a laid-back and relaxed personality, and is never hard on his teammates, even when they continue to make mistakes. Members quitting the club traumatized him, so he was unable to be harsh.
- Oyama's nickname, "Tai-san", comes from the elementary school game "Oyama no Taishou" (King of the Mountain). He kept this nickname through high school.