Defenders who guard their own way, and passes that find a player on the move

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 the players who are not holding the ball, which on a basketball court is nine of the ten, nearly all of the time.

Every defender keeps their own distance

A defender guarding a player without the ball has a choice to make all the time: stand close to their own player, or step off toward the ball and the basket, ready to help a teammate if someone drives in. Coaches have a textbook spot for it, a point between the player, the ball and the basket. Real defenders do not stand there exactly. Measured in tracking data from real games, they stand about a foot looser than the textbook spot on average, and, more interesting, how loose is a habit of their own: some defenders always guard tight, some always sag off, and the same defender does it again game after game.

Until now every defender in the league stood on the textbook spot. Now each one has their own looseness, drawn from the spread the real measurements found, and it decides where they stand once both teams are set up at one end of the floor. So two defenders guarding the same shooter leave different amounts of room, and an alert passer can find the one who left more. In the twelve test games behind this change, the nearest defender to a player catching the ball beyond the three-point line moved from about 8 feet away to about 9, against about 9.3 in real games.

Defenders go around each other, not through

Bodies here are meant to be solid: two players should not stand in the same place, and the game counts every possession where they do. Giving every defender their own spot had a side effect we measured straight away: defenders crossing the court to their new spots ran through their own teammates more often, which is not something you should ever see in a replay. The cure was not to move the spots but to teach the runs: each defender now picks a path around the teammates already in the way. Possessions where two defenders were ever inside one another fell from about one in four to about one in nine, where they stand today.

A pass that leads a player on the move

In real basketball, most catches away from the basket are made by someone still moving: a shooter stepping into a pass, a teammate drifting to an open spot as the ball swings round. In the tracking data, three in four catches beyond the three-point line are made on the move.

In this league a player stepping to a new spot used to be invisible to the passer until they arrived, so nearly every catch was made standing still. Now a player on the way to a spot they chose is someone the passer can see and weigh, the way a teammate cutting to the basket already was, and the pass is thrown to meet them on their way, never at a point before they can get there. In the twelve test games behind this change, catches made on the move beyond the arc went from 6% to 22%, and just inside it from 12% to 41%. Real players still catch on the move more often than that, so the league's shooters stand a little more still than real ones do, but you can now watch a shooter step into a pass and let it go in one motion. The same change routes those players around each other too: teammates on offence end up inside one another in about one possession in twenty, down from one in eight.

Why it matters for watching

Where the players without the ball stand decides almost everything about the player with it: who is open, which pass is safe, whether a drive has a helper waiting. Building those positions from each defender's own habits and each player's own runs, instead of from one rule for everyone, is what this league is for. Pick any game on the front page and watch the players away from the ball: the space each defender gives is their own.