The balls, shaped like the traditional Japanese ‘onigiri’ rice ball wrapped in seaweed, were fired at goalkeepers during training at the weekend, local media reported on Monday.
“It was good practice,” goalkeeper Takuya Masuda told the Nikkan Sports newspaper after a dizzying session trying to stop the oversized lunch snacks.
“Hopefully we can apply it in matches.”
Goalkeeping coach Hisanori Fujiwara said: “The ball is irregular in shape so it behaves irregularly through the air too. It sharpens reactions and helps improve concentration.”
Japan, who employ various innovative training methods, including playing with volleyballs, face Spain on July 26 in their opening Group D match at the London Olympics before meeting Honduras and Morocco.