He said peer pressure was a powerful social force.

“In this case, the primary motivation isn’t so much a desire to keep the stadium clean or to avoid causing trouble for the people who have to clean the stadium afterwards,” he said. “It’s more a desire not to be seen as a nuisance in one’s own group.”

Whatever the reasons, Japan’s fans will keep tidying up for as long as they stay in the tournament.

Their next game is against Tunisia in Mexico on Saturday, and fan Hagiwara is happy to keep leading by example.

“We usually don’t tell children they should do it,” he said. “We just show our actions and behavior, and other people follow.”