TOKYO — On a cloudless spring afternoon, thousands of parents, teachers and alumni watched as a pack of young students charged across a field, screaming and snarling, and then crashed into a wall of students defending an 11.8-foot wooden pole. The attackers clawed, shoved and jumped over the opposition. Heads butted. Elbows were thrown. The wall buckled, then stood firm. Like a mast on a sailboat in rough seas, the pole dipped, then rose again.

This wasn’t trench warfare, it was botaoshi, a century-old game that combines elements of American football, rugby, sumo and martial arts. The game has gotten so dangerous that many Japanese schools have abandoned it, but it lives on at Kaisei Gakuen, where it is the centerpiece of the school’s annual sports festival.

Little known in America, botaoshi, or “topple the pole,” remains a rite of passage at Kaisei, which opened in 1871 and is one of Japan’s most prestigious secondary schools. Teachers say the game promotes teamwork, toughness and sportsmanship. Students eagerly await their chance to compete in the tournament in their junior and senior years. (Underclassmen play more rudimentary games.) Alumni can recount details of games played decades ago.