A violation called when the offense fails to bring the ball from the backcourt to the frontcourt within eight seconds after gaining possession. When the violation is called, the offense loses possession of the ball and the opposing team inbounds the ball from the sidelines. The player in possession of the ball when the violation is called is charged with a turnover.
When defenses apply full court pressure, one of their goals is to harass the ball handlers long enough so that they don't cross the half court line in less than eight seconds.
Before the 2001-02 season, the players in the NBA were allowed 10 seconds to advance the ball from the backcourt to the frontcourt. However, in order to generate a more up-tempo style of basketball, the NBA changed the backcourt violation rule to eight seconds.