Yamaguchi Tadashi.

The match against Inarizaki had ended surprisingly well; Karasuno emerged victorious 2-1. Sadness and stress were evident on the faces of the Miya twins, but it wasn't as if Yamaguchi cared about it, as the first thing he did was run towards Tsukishima and throw himself on top of him, caught up in the euphoria of the moment.
She cried, screamed, kicked... until they calmed down a bit. They did what they always do: finish the game and thank the players.
Yamaguchi was about to leave, but stopped when he heard one of the Inarizaki players—Atsumu Miya—speaking to Hinata. He frowned, confused, but decided not to dwell on it.
"Hey, you, the one with the float serve." A deep voice, identical to Atsumu Miya's, called to him.
Yamaguchi stopped again, turned to whoever was calling him, and his eyes widened slightly in surprise when he realized that Osamu Miya was calling and pointing at him just as his younger brother had done with Shoyo.
"Someday, I'll invite you to dinner," said the gray-haired man, then turned around and left as if nothing had happened while he was arguing with his brother.
The freckled boy tilted his head, completely confused; but a blush soon appeared on his freckled cheeks unconsciously. He was completely speechless. What he didn't notice was his best friend at the end of the court watching the whole scene with a serious, almost angry face.
(You're Tsukishima!)

Yamaguchi doesn't pick up on hints, although he's not completely stupid; he knows that Osamu flirted with him blatantly, but he's undecided; he doesn't know whether to have dinner with him or stay with his first love, Tsukishima.