The weak side picks the coverage before the ball does

Defenses choose how to handle a ball screen by reading the two players furthest from it, which is why decoy alignment works.

Ask an assistant coach how he decides between switching and dropping and he will start talking about the ball handler. Ask him again after three drinks and he will admit that most of the decision was made by looking at where the other two offensive players were standing.

That is not a criticism. It is the correct read. A weak side with two shooters spaced above the break means help has to travel a long way and arrive at speed, so you would rather switch and keep everyone attached. A weak side with a non-shooter parked in the dunker spot means you have a free defender, which makes any help-heavy coverage viable, including a hard blitz you could not otherwise afford.

The offensive implication is that you can lie about your intentions with alignment alone. Put your worst shooter above the break on the weak side and the defense reads shooter-heavy spacing and switches, then bring him down late and run the action into a coverage chosen for a floor that no longer exists. Two seconds of misinformation is enough. Defensive calls are made early, and they are extremely hard to change once four people have started moving.

This is also why I distrust any analysis of ball screen defense that identifies the coverage from the two defenders near the ball. The coverage is a property of five players and it was determined by the shape of the floor a full three seconds before the screen arrived.

Teams that understand this run their weak-side movement as a real part of the action rather than as spacing decoration. It is harder to coach because it requires the two players furthest from the ball to care about a possession they may never touch.

This is why I get suspicious of the phrase reading the defense, which implies a single moment of perception when the ball handler comes off the screen. By then the reading is over. The read that mattered happened when the offense chose its alignment and the defense chose its call, and everything after that is two groups executing decisions they already made against information they already had.

Most bad offenses are not badly designed. They are correctly designed and then stood still in the wrong places.