Basketball
How Off-Ball Screens Create Advantages Without The Ball
Screens set away from the ball move defenders who are not watching it, and the resulting advantage often appears two passes later rather than immediately.
Most attention on a possession follows the ball. A large share of the advantages an offence creates are generated by two players working somewhere else entirely.
Defenders away from the ball are split in attention
A defender guarding a player without the ball must keep both his assignment and the ball in view, which usually means positioning himself to see both at an angle.
That posture leaves him partially turned, so a screen arriving from his blind side is difficult to see and even harder to navigate.
Off-ball screens exploit that specifically, being set from the side the defender is not facing so the contact is a surprise rather than an obstacle he can prepare for.
The screen forces an immediate choice
A defender caught on a screen can go over it, under it, or switch, and each option concedes something specific to the cutter.
Going under concedes a catch-and-shoot opportunity, going over concedes a curl towards the basket, and switching concedes whatever mismatch the exchange produces.
Well-coached cutters read the choice as it happens rather than running a predetermined route, which is why the same screen produces different actions on different possessions.
Help responsibilities create the second advantage
When a defender is beaten by a screen, a teammate must help, and that help leaves the helper's own assignment momentarily unguarded.
The offence's advantage therefore transfers, and the open shot often belongs to a player who had nothing to do with the original action.
This is why possessions are designed as sequences rather than as single plays, with the initial screen intended to start a chain of defensive rotations.
Staggered and double screens multiply the problem
Two screeners in succession force the defender to navigate twice, and the second screen usually catches him at the moment he has recovered from the first.
Defending this requires communication between three defenders, and the switch responsibilities must be resolved while all of them are moving.
Offences use the screeners themselves as secondary threats, since a defender who commits fully to helping on the cutter leaves a screener free to roll or pop.
Spacing determines whether any of it works
Off-ball screening only produces open shots if the defenders who might help are occupied by shooters they cannot afford to leave.
A team with non-shooters standing in help positions gives the defence free bodies, and those bodies erase the advantage the screen created.
The proliferation of shooting across all positions is therefore what has made off-ball screening effective, rather than any change in the screening technique itself.
