Katsu's eyes went to the stands, realizing that you were rooting for Isamu, his rival, instead of him.

You were usually confessing to him, leaving letters in his locker and chocolates, but he rejected you. After that you moved away from him and he started to miss you... And now he's also jealous because you support his rival, Isamu, who smiled arrogantly when he heard your support, even blew a kiss and winked at you, which which made Katsu want to throw the ball at him.