Defenders guard where the play is going, not where it was

basketball.casa is a basketball league where every game is simulated. Nobody scripts the plays. Each one comes out of who the players are at that moment: how tall, fast and tired they are, what they can see, and what they decide. You can watch any game back exactly as it happened. This update is about defence, and about timing: a defender who moves now moves for where the play will be, not where it was a moment ago.

Running to where the player will be

When the ball moves, every defender picks a spot to go to, near the player they are guarding. Until now that spot was worked out from where the player stood at that moment. But players move too. After a pass, an attacker often relocates to a new spot on the floor, and a defender heading for where they used to be could end up right in their path, the two of them running into the same space.

Now a defender heads for where the player will be by the time the defender gets there. It only works for what they can see: a defender who has the player in view reads the run and meets it, and one who is looking elsewhere goes to where the player was, as before. So a defender's sense of the floor matters a little more than it did.

Across a test set of 24 games, the runs where a relocating attacker ended up inside a defender's path fell from 131 to 107, out of about 6,900. And on a catch-and-shoot three, the nearest defender is now about 3.6 metres away as the ball is caught, down from 3.8, close to the 3.7 metres that tracking studies of real games measure. Nothing was tuned to hit that number; it moved because the defenders now read the play.

Round the rebounder, not through them

A smaller fix landed alongside it. When the attack wins an offensive rebound, the defence scrambles back into place. Their runs used to be routed round the spot where the rebounder would end up, not the path the rebounder takes to get to the ball, so the two could cross on the way. Now the defence goes round the whole run. In the same 24 games, the crashes where a rebounder ran through a defender fell from 16 of 181 to 10.

Why it matters

Ten bodies share one floor, and every one of them is deciding where to go based on what the others are doing. The closer each decision gets to what a real player would see and do, the more a replay looks like basketball rather than ten people following lines. Watch a defender after a pass: they no longer chase the spot their player has left.