Rollergirls

Tattoos, skates, and arena lights.
There's a fast parade of black and red butterflies, action upon reaction.
There's physics at play here.
Examples of internia, in which 130 pound bodies moving at a horizontal vector against gravity's pull, are slammed into eachother. Sometimes the force is so great that gravity takes over and the floor becomes closer to the skater than ever before.
The result is a chain reaction of the floor coming into quick contact with knees, elbows, heads, fingers, joints, and chins.
Although the pain is there, some parts never really touch, divided by a thin piece of natural or man made fabric.
Like winding up a clock, chaos comes to an end, and order is restored.
The whole theory starts again, proven by the result of sweat, scrapes and bruises.