Question: why does oikawa hate kageyama?
Answer: Oikawa's hatred of Kageyama got to the point where he nearly hit Kageyama, but Iwaizumi stepped in at the last minute. He yelled at Oikawa for his behavior and the two started arguing because Oikawa believed that he had to keep getting stronger in order to beat Shiratorizawa and Ushijima, his longtime rival.