Real Ultimate Snowball Battle
In Japanese Hands, Snowball Fighting Has Really Grown Up
On winter evenings, men gather outside a hotel in Japan’s frozen north to heat snow with an oil stove in a vinyl tent. When the powdery stuff becomes malleable, they shovel it into a mold resembling a giant cupcake tray, and stamp out 1,000 perfectly round snowballs of regulation size: no less than 2.56 inches in diameter and no more than 2.76 inches.
Here’s where you can buy the regulation practice snowballs (46g nylon covered beanbags):
I also found this collection of videos explaining the game, This one covers some of the basic rules.