Ball screens have progressed from the days when I was a kid ("Set a screen for me so I can get my shot") to an intricate action that can show up at any time in any offense. They are used as offensive entry actions, space creators and most importantly to control matchups. They have been part of basketball since Dr. Naismith hung his peach baskets in the Springfield, Ma. YMCA and invented the game. Since Michael Jordan changed the game to a "matchup and isolate" game, ball screens have become a bigger and bigger part of the game. If you don't learn how to defend them, you are at a severe disadvantage.