The first thing a young defender learns, shown inside a whole possession: the stance (feet wider than the shoulders, butt down, back straight, hands active, nose on the ball handler's chest) and what it does to a possession. The offense runs five-out, swings the ball to both wings, and drives twice; each time the on-ball defender slides without crossing his feet, stays an arm's length away, and turns the dribbler sideways instead of letting him go downhill. Why the stance matters more than anything else at this age: a dribbler who is turned sideways has to pick up his dribble, and a dead ball is the best outcome a defense can force without a steal, because the offense has to pass out of it and start over. What the on-ball defender concedes: the pass. What he never concedes: the straight line to the rim. Where the advantage lies: every drive that ends in a pick-up costs the offense three seconds and gains it nothing, and five of those is a possession that ends in a contested shot. Common youth mistakes: standing up straight, reaching for the ball (the reach is a foul or a blow-by), crossing the feet, and watching the ball instead of the chest. I picked the stance teaching up from Darren Erman's Jr. NBA session and Coach's Clipboard's basic defensive tips; give both a look if you want more on the footwork.
