Right-handed pitcher Shumpei Yoshikawa has signed with Major League Baseball's Arizona Diamondbacks and broken amateur baseball rules in the process, informed sources said Friday.

Yoshikawa was expected to go high in Nippon Professional Baseball's amateur draft this October. He is the first marquee amateur to skip NPB and sign directly with a major league club since pitcher Junichi Tazawa signed with the Boston Red Sox in December 2008.

(Shumpei Yoshikawa)

Japan's amateur baseball federation requires players have their player registrations deleted the day before they enter into a pro contract, but his corporate league team, Panasonic, announced Friday that Yoshikawa had violated that rule.

It is said that Yoshikawa began contract negotiations with the Diamondbacks before filing the proper documents -- and was in touch with the American club even before the end of the recently completed intercity tournament.

Both Yoshikawa and the director of Panasonic's baseball department have said they were unaware any rules had been broken.

Major league teams ostensibly have better access to Japanese amateur players than their Nippon Professional Baseball counterparts. This is due to NPB teams flouting amateur baseball rules in the past, including signing amateurs during the season and paying off amateur players.

By signing with the Diamondbacks, Yoshikawa has essentially excluded himself from ever playing for Japan's national team in the World Baseball Classic. In the days prior to Tazawa's signing with the Red Sox, NPB tried to blackmail him by instituting the infamous "Tazawa Rule." This rule effectively bans a player from ever playing in NPB or for the national team.