Watch the rough-and-tumble Flint City Derby Girls in action

You'll either want to join them.

Or get the hell out of their way. 

Either way, the Flint City Derby Girls are pretty amazing. And, as you can see in the video above, there is nothing delicate about them.

This is roller derby. It is all about hitting, knocking, tripping, bruising. 

Related: Meet the tough girls who roll with Flint City Derby

"These are all the women that you see in your everyday life that you would never expect to take a hit like they do or to give a hit like they do. These are like the sweetest women you've ever met, like singing at church, and then they come and kick my frigging butt," said Ashley MacDermaid, aka Ash Tray. 

Here's the thing though ... that's kind of part of the appeal.

MacDermaid remembers the first time she ever saw roller derby in action. "It was insane. It was the most beautiful thing I've ever seen. ...  There is hardly any fighting in sports," she says.

At least in other sports.

Roller derby was different. It uses strategy and brute strength, and fighting is a basic premise of the game: "It was exactly what I wanted to do," MacDermaid says.