As quickly as Pierce was earning a reputation for her hard-hitting forehand, her father was becoming infamous for his abusive and berating behavior. He bragged about how hard he worked his daughter, telling The Sporting News in 1993, "For seven years, eight hours a day, I hit 700 serves at Mary. We usta work until midnight. My young son slept by the net. I wouldn't let Mary leave until she got it right. Sure, she cried. I cried, too. So what?" He controlled everything, including her diet, her workouts, and her friends. Pierce told Sports Illustrated "He was always very tough, but the more and more I was winning, the better I was doing, the tougher he got." Even early in her career, Pierce's father was openly abusive both to his daughter and anyone else who happened to be in his line of fire. In 1987 Pierce was playing 12-year-old Magdalena Maleeva in a tournament when her father screamed from the stands, "Mary, kill the bitch!" In response, Pierce threw h! er racket in her father's direction. As a result the Florida Tennis Association banned Jim Pierce from attending its tournaments for six months.
In 1988 the highly regarded Harry Hopman Tennis Academy in Wesley Chapel, Florida, refused to renew Pierce's scholarship because of her father's behavior. Pierce turned professional just three months after her fourteenth birthday in 1989. At the time she was the youngest professional ever. (The following year Jennifer Capriati turned pro at the age of thirteen.) In 1990 the United States Tennis Association (USTA), who had been working to provide Pierce with financial and coaching support, withdrew funding because of Jim Pierce's volatile and abusive behavior that routinely included courtside tantrums and verbally berating his daughter, lines judges, opponents, and fans. Claiming that he was fed up with the USTA's lack of support, Jim Pierce moved the family to France where Pierce and her French-born mother had citizenship. Pierce received financial support in exchange for playing on the French Olympic and! Federation Cup teams.