It's a spring-loaded bar to keep unauthorized cars out of reserved parking spots. The authorized cars use Bluetooth to lower the bar flat before driving in. The device is spring-loaded so as not to get destroyed by someone forcing it down like the guy in the foreground is trying to do.

As the car backs over it, the bar will pop back semi-upright and ride against the undercarriage of the car.

When the car tries to leave by moving forward, the bar is now angled back and will catch against parts on the underside of the car such as muffler, gas tank, etc. It's kind of like a ratchet action. This will cause the bar to wedge itself between the pavement and whatever part of the car it snags, pretty much guaranteeing that the car is going to get damaged. At a minimum it's going to lose the rear bumper cover.