You can check out some prior posts on this subject. It's a popular one.
When dribbling the ball from the backcourt (BC), the player needs to get both feet AND the ball into the frontcourt (FC) before FC status can be established. So, as long as one of those three are in the BC, then the player is in the BC (10 sec. count continues, too).
I.E. He can dribble the ball in the FC and back to the BC if he keeps at least one foot back there.
It is a good technique to draw a trap early when you come across half court near the sideline. The def. coach will want two of his players to "box in" the dribbler with the sideline and midcourt line (MC) to trap him. Dribbler "shows" the ball over MC while keeping one foot in BC...trap comes, he pulls ball back and goes around them...