What is that big thing around the treadmill? Anyone knows?

Apparently it is the Anti-Gravity Treadmill. From their website:

Take your athletes higher with AlterG technology

Uses patented Differential Air Pressure technology to unweight your athletes to as little as 20% of body weight in precise 1% increments for low-impact, pain-free movement.

Supports normal gait mechanics and avoids development of compensatory strategies.

Real-time gait data, pain recording, and live video monitoring improve decision-making on the fly with objective, measurable information and visual feedback.

Limit downtime by training through injuries and enabling a return to sport in better condition.

Enable earlier post-surgery training.

Increase training volume while minimizing stress-related injury.

Encourage early restoration of lower extremity range of motion, shown to improve outcomes.

Apparently it is the Anti-Gravity Treadmill. From their website:

Take your athletes higher with AlterG technology

Uses patented Differential Air Pressure technology to unweight your athletes to as little as 20% of body weight in precise 1% increments for low-impact, pain-free movement.

Supports normal gait mechanics and avoids development of compensatory strategies.

Real-time gait data, pain recording, and live video monitoring improve decision-making on the fly with objective, measurable information and visual feedback.

Limit downtime by training through injuries and enabling a return to sport in better condition.

Enable earlier post-surgery training.

Increase training volume while minimizing stress-related injury.

Encourage early restoration of lower extremity range of motion, shown to improve outcomes.

Wow that's some cool stuff. I can totally see the benefit of not having to put your full bodyweight on the injured knee right away. Probably enables him to start running earlier than what had been the case otherwise.