Sam Subby provided us with a nice backcourt or not clip earlier this week. We had a lot of input on that one.
For the ball to be on offense we have to have both feet of the player and the ball on frontcourt. A player having both feet on offense holding the ball will give you a ball that is considered to be on frontcourt. Back to the clip: the player dribbling (and thus controlling the ball) has two feet on front court before he steps back to backcourt with his left foot. That way the ball goes back to backcourt which is illegal: See OBRI 28.1.2 second dot: The team has caused the ball to go into its frontcourt whenever: ‘The ball touches sor is legally touched by an offensive player who has both feet completely in contact with his frontcourt.