career-high 40 points against the Denver Nuggets on 17 of 25 shooting. Mayo was late for a game-day shootaround and was taken out of the starting lineup starting November 20, 2010. On a return flight to Memphis from Los Angeles, Mayo was involved in a fight with teammate Tony Allen over a debt from an in-flight card game. On January 27, the NBA suspended Mayo for 10 games following a positive test for the steroid dehydroepiandrosterone (DHEA), which violates the league's anti-drug program. Mayo blamed an over the counter supplement that he didn't know was banned by the NBA for the positive test, but he declined to say which supplement he used. He later said an unnamed energy drink he bought at a gas station contained the banned substance. Despite playing in all 66 games of the shortened 2011–12 season, Mayo did not start in any games for the Grizzlies, playing as a sixth man. When he was asked if being a reserve hurt his value, he answered, "I would say so, I would probably say so. What do you think?" Dallas Mavericks (2012–2013) The Grizzlies did not sign a qualifying offer sheet for Mayo, making him an unrestricted free agent. On July 19, Mayo officially signed with the Mavericks. On December 8, Mayo tied his career-high of 40 points in a game against the Houston Rockets. Two days later, he tied a career high of playing 52 minutes in a double-overtime loss to the Boston Celtics. On December 28, 2012, Mayo had a career high of 5 steals against the Denver Nuggets. On March 6, Mayo recorded a new career high of 12 assists against the Houston Rockets. After Nowitzki, the Mavericks' all-time leading scorer, returned, Mayo saw his scoring average dip. Mayo said, "I'm a scorer and can shoot the ball a little bit, but I like to be a playmaker. I like to try to take what the defense gives you and not just concentrate on scoring the ball. Find other guys." Mayo finished the season with averages of 15.3 points, 4.4 assists and 3.5 rebounds while playing a team-high 35.5 minutes per game. His production dropped considerably after the All-Star break, when star player Nowitzki re-emerged after missing the first 27 games. On April 18, 2013, he announced he would decline the player option on his contract for the following season and become a free agent.