G1 Brunson is a Unitree G1 humanoid taught, by trial and error inside a physics simulation, to do the between-the-legs crossover with a regulation basketball. No sensors on the ball. It sees it with its own head camera.
This is the recorded test episode, not an animation: the actual G1 meshes from Unitree's robot description, driven by the joint angles the controller produced, frame by frame. Drag to orbit, scroll to zoom, scrub the timeline. Orange ticks are bounces that landed between the feet.
Each run is a training session on a rented GPU. Each one taught us something, usually by breaking. The bar is the number of crossovers per 20-second test.
Reinforcement learning is just: do something, get a score, do more of what scored. The whole trick was writing the scoring rule so that only a real crossover pays. Flip the switches to see how one bounce gets scored.
These frames are rendered by MuJoCo from the robot's head camera during the recorded test, then run through the shipped perception module. Nothing here is illustrated by hand. Pick a stream; it plays on its own, scrub to pause.
The D435's depth stream is the primary sensor (87° × 58°, wider than the colour stream). Near is bright. It does not care about lighting or floor colour.
The robot renders what its own body should look like from its joint angles and removes it from the depth image. The floor cancels too. Whatever is left and closer than the body is the ball.
A sphere of the known radius is fitted to the remaining pixels, giving the ball's centre to about 2 mm. When the ball is hidden under the body (white circle), a Kalman tracker with a bounce model carries it through.
HIM Arena's Open Build challenge asks for a humanoid skill that is grounded in real physics, evaluated honestly, and shipped as a package anyone can run: a policy, a simulator, and a writeup. Here is how G1 Brunson answered each line of that brief. Click a card.
Three paths: run the test on a laptop in five minutes, retrain from scratch on one GPU in about a day, or put it on a real G1. Tick the boxes as you go; the page remembers.
Built in the afterglow of the Knicks' championship run. Jalen Brunson keeps the ball low, tight and on a string, and never looks rushed. That is what we were trying to get out of a robot with rubber hands. G1 is the robot, Brunson wears 11. Two ones. We noticed after naming it.
Click the jersey. Not affiliated with the NBA or the Knicks, just fans.