Conservative world of sumo slow to take action on concussion

While football and rugby make adjustments, clashes of heads continue in Japan's national sport

The crack of two skulls colliding echoed around the sumo arena. One of the wrestlers returned to his starting position in the ring, apparently unfazed. But his opponent, Shonannoumi, was clearly in distress.

Is he OK?" asked the TV commentator after Shonannoumi's leg buckled as he attempted to raise his 164kg (25st 11lb) frame from the ground. The referee and judges exchanged looks but with no ringside doctor to consult none seemed sure how to react.