Marvin Miller headed the union effort that allowed players to choose new teams when their contracts ended, ushering in an era of multimillion-dollar free-agent deals. Miller, who ran the Major League Baseball Players Assn. from 1966 to 1983, was 95.Marvin Miller, the feisty union leader who guided baseball players into an era of mega-salaries and free agency, thereby helping to change the landscape of American sports, has died.