Jars of "sacred" soil apparently taken from Koshien Stadium — the mecca of Japanese baseball — have been sold online via the popular flea market operated by Mercari Inc., stoking controversy as excited viewers nationwide tuned in to the annual summer High School National Baseball Championship.

During the tournament, which wrapped up for this year on Tuesday, it is customary for the defeated team to scoop up handfuls of dirt from the iconic field, which is the dream stage for every young Japanese ballplayer, as mementos to take home.

The soil appears to have been traded in jars, with pictures showing that some was sold at prices of between ¥1,000 and ¥3,500. Notes attached to some of the jars claimed that the soil "was brought back" by players from losing teams, while others claimed that the heirlooms were obtained from their seniors — indicating that they may be from past tournaments.

Mercari has not banned the trading of the items, saying there is no breach of their rules, but the move has triggered concern over possible fakes.

The app operator has said it is urging sellers to clarify how and when they obtained the soil, though it has no plan to confirm whether the items truly come from the stadium in Nishinomiya, Hyogo Prefecture. "We are asking our customers to think carefully before buying," a company official said.

Some critics have said young boys who dream of making it to the grand stage at Koshien may end up purchasing fakes.

Asked for comment, an official with the tournament headquarters said it was "not in a position to comment on the issue."

According to the Koshien Stadium website, the baseball field consists of sand and black soil taken from areas including Okayama, Mie and Kagoshima prefectures.