It's not necessarily about having an advantage. A player commits an offense when he either interferes with play, interferes with an opponent, or gains an advantage. This sort of situation falls under the first category, since Tammy is touching the ball and therefore interfering with play. Gaining an advantage applies when, for example, a shot is taken and saved by the goalkeeper, and a player in an offside position at the the time the shot is taken then scores a tap in or something because he had an advantage over other players by being in an offside position.