All world open tournaments operate under knockdown karate rules which involve standup bareknuckle fighting with basically no protection.
The more characteristical rules in knockdown karate compared to other styles are that you are not allowed to punch in the face and a point system that only counts hits that actually "hurt" the opponent.
This makes knockdown fighting very physical but at the same time quite safe considering that there are very few hits to the head.
The event was held five times: After the death of Mas Oyama in 1994, IKO split up into several factions.
The World Open Tournament has continued to be held but organised in parallel by several organizations.