He explained that NBA players make free-throws about 75 percent of the time and make shots within 3 feet of the basket 61 percent of the time. Almost every other shot, from 3-pointers to mid-range jumpers, goes in about 37 to 38 percent of the time.
Therefore, he tells his guards that they must sprint back on defense whenever a teammate attempts a shot; that way, the opponent won't get many uncontested layups. It's also critical for the defense to keep the ball out of the paint, because that's where layups and most of the fouls occur.
The first point in the final paragraph, about guards conceding defensive rebounds in order to prevent fast breaks, is particularly salient. Despite having Dwight Howard, the league's leading overall rebounder, the Magic have ranked 27th and 28th in offensive rebound percentage in Van Gundy's two seasons with Orlando. Whatever they lose on the offensive glass, they gain on the defensive end, having placed 6th and 1st in defensive efficiency during those seasons. Rarely do opponents exploit Orlando on the fast-break, which justifies--to an extent--its poor statistical showing with regard to offensive rebounding.
Josh Robbins of the Orlando Sentinel reporting on Stan Van Gundy speaking at the Florida Association of Basketball Coaches via a blog post by Ben Q Rock