With close to 60 games already played, Nippon Professional Baseball acknowledged for the first time that a new ball was being used. The new livelier ball has resulted in more home runs.
"We had an idea something was different this season," Rakuten Eagles catcher Motohiro Shima said Wednesday. "Here we are almost 60 games into the season and now they tell us? It's very unfortunate."
NPB had previously denied that this year's increase in home runs had anything to do with changes to the baseball.
NPB also instructed the ball's manufacturer, Mizuno Corp., to say no changes were made if anyone asked.
NPB said the balls used last season did not meet certain standards and the new ball was introduced to conform to the rules.
Before the start of the 2011 season, different balls were used by the Pacific and Central Leagues. In 2011, NPB introduced a uniform ball to meet international standards.