Millar played for the Marlins from 1998 to 2002, and was later sold to the Japanese Central League Chunichi Dragons. In order for the transaction to be completed, he first had to clear the waivers requested by the Marlins, but the Red Sox broke an unwritten rule and blocked the deal with a waiver claim. In an unprecedented deal brokered by MLB, the Marlins later repaid the money that the Dragons had paid for Millar, and the Red Sox paid a similar sum to the Marlins in return for Millar. His clubhouse presence and offensive production helped spark the Red Sox to the 2003 American League Championship Series and the 2004 World Series.