A controversial tackle by a Nihon University football player became a police matter Monday, as the family of the injured player filed a criminal complaint.

The dangerous tackle against a Kwansei Gakuin University quarterback has sparked nationwide criticism and led Nihon University coach Masato Uchida to announce his resignation on Saturday, but the coach did not say whether he had instructed foul play.

"I am confused as there were no explanations about why the Nihon University athlete played in that manner and whether he had been instructed," said the injured player's father in a statement released by Kwansei Gakuin University on Sunday.

During a game on May 6 in Tokyo, the Nihon University player tackled the Kwansei Gakuin quarterback from behind long after he had released the ball. The tackled player sustained ligament damage in his spine that will take three weeks to heal.

Kwansei Gakuin and Nihon University, also known as Nichidai, have long been archrivals on the college gridiron.

A video of the play went viral and drew a backlash in Japan, prompting many schools to cancel games against Nichidai. The government's Japan Sports Agency also launched an inquiry over the case.

"We want to know what led to the dangerous tackle rather than (hear about) a resignation," JSA chief Daichi Suzuki said Sunday.