The 4-6-3 is the closest thing baseball has to a crossing pattern, or a screen, or a set play at all. Obviously, there are relays all over baseball, but those are relays: I want to throw it over there, you’re on the way to over there, so I’ll throw it to you and then you’ll keep the line moving. Even a 5-4-3 or a 6-4-3 is basically just moving the ball toward first, with a quick stop on the way. But the 4-6-3 is a strategic anomaly, the only routine play that crosses over itself: The second baseman throws the ball away from its ultimate destination, knowing the shortstop is coming toward him to redirect it. The journey of the baseball from home plate, on pretty much every baseball play, can be drawn as either a straight line or as an upside-down V. But the movement of a 4-6-3 double play draws a 4
Source: Sam Miller, ESPN.com