Nippon Professional Baseball received an official warning on Thursday that its rules regarding player agents may be illegal. The Japan Fair Trade Commission stated a concern that the NPB rule requiring player agents to be lawyers may violate antitrust law. The rule was abolished by NPB on Sept. 2. According to the commission, NPB decided in November 2000 to allow players to employ agents in their contract negotiations with teams but required each agent to be a lawyer who could represent only one player. The rule allowing agents came about after pressure from the players. The commission began i…