The incident occurred during a game between Kwansei Gakuin University and Nihon University on May 6th. A Kwansei Gakuin quarterback suffered a knee injury and had to leave the field. Medical staff expected him to be out of action for up to three weeks.
Hiromu Ono, a coach of the Kwansei Gakuin University team spoke to reporters: "The tackle was intended to hurt our player. It was a very dangerous and despicable act that has no place in American football."
Ex-NFL pro Masafumi Kawaguchi says he's never seen anything like it:
"Tackling a player holding the ball is permissible, even from behind, but it's hard to believe someone would tackle a quarterback from behind several seconds after he's passed the ball.
"And tackling the lower part of the body is also unbelievable."
Fact-finding
Daichi Suzuki, Commissioner of the Japan Sports Agency, says "We need to look into the facts and the background of the play to prevent a recurrence."
Nihon University says it has questioned its coaches and the player involved and handed a report to Kwansei Gakuin. The university says the report contains the details of what happened, as well as an apology.
The Japan American Football Association issued a statement calling for comprehensive measures to prevent dangerous play.
It says American football is a full-contact sport, but players are not allowed to intentionally injure their opponents.
Powerhouse teams
Both Kwansei Gakuin University and Nihon University are powerhouses in Japan's college football. Kwansei Gakuin has won the Koshien Bowl -- Japan's national championship -- 28 times, while Nihon University has 21 titles.
Last December, the teams faced off for the 29th time at Koshien Stadium. Nihon University picked up its first national title in 27 years, beating the defending champion 23 to 17.
Tadayuki Murata is Ryukoku University's head coach. He was working for television at last year's Koshien Bowl.
Murata says he got the impression that Nihon University played hard, but fair. He says he was genuinely surprised by the incident earlier this month, which seemed out of character.
He says everything he saw at last year's game suggested the offending player was clean.
However, in May, the Nihon University player in question was ejected from the game after repeated rough and dangerous acts.
His coaches didn't seem to criticize him when he walked to the bench. They even seemed to thank him.
People with the Kwansei Gakuin team were stunned.
Team director Hiromu Ono says the opposition coaches didn't appear to be upset at their player, despite his repeated infractions. He says it never happens on his team.
New Orleans Saints
Six years ago in the US, ABC TV reported that a coach of NFL team the New Orleans Saints encouraged his players to try to deliberately injure opponents.
It was discovered that players were paid reward money if they succeeded.
NHK TV commentator Tadayuki Murata says that incident prompted a push for fair play in the sport in the United States.
He says: "That kind of thing shouldn't have happened in the NFL. It runs against the principle of sportsmanship to try to win by harming opponents.
"Coaches must teach their student players that the top priority is fair play. That's a fundamental value of all sports. A full investigation must be made into the facts of the incident."
After a detailed medical check the injured player was given the all clear and is unlikely to suffer any lasting damage.
Minimizing danger
The impact of frequent concussions on the health of American football players has become a hot topic in the US and other countries.
American football federations across Japan hold frequent seminars. They are designed to teach college players and their coaches the appropriate ways to tackle and block opponents without relying on helmets, as well as how to deal with concussions.
Rules have also been revised to ensure player safety, with penalties for those making bad tackles getting tougher.
Kwansei Gakuin has been placing greater importance on safety than on winning games since one of its players died during training in 2003.
It started an annual safety program and drew up a manual on how to handle players suffering from concussion.
Now, however, the tackle made by the Nihon University player is facing mounting criticism, particularly as it flies in the face of the trend toward improving safety on the field of play.