Although the source link does no longer work, the following is quoted from the NHK. The event took place on the 7th of April 2013. A video of the battle is available on Belgian site Karrewiet.
800 children have taken part in an outdoor match of kendo sword-fighting in Yamanashi Prefecture, west of Tokyo.
Sunday’s match was part of an annual event commemorating the death of Takeda Shingen, the 16th-century warlord whose domain overlapped Yamanashi. He is said to have died on April 12th, 1573.
The children aged between 3 and 18 were divided into eastern and western teams. They attached red or white balloons to their face guards to show which team they belonged to.
When the match started, the children ran to their opponents and swung bamboo swords to pop the balloons.
The match ended with no winner. This is in tribute to Shingen and his rival warlord Uesugi Kenshin, who fought each other several times without a decisive victory.
A junior high school girl said she took part for the third time and enjoyed the event because it’s different from the usual kendo matches.
The chief of the organizing committee says he wants to promote kendo among children and make the outdoor match even bigger.
The idea of a balloon tournament is of course nothing new and it’s been done before. Case in point, the wonderful four-team battle shown below. In many western dojo the balloon battles have become a staple event for holidays (New Year’s, Halloween, etc).
Renshinjuku Kendo
800 child kendo battle