The peroneal tendons help stabilize your foot. They're kind of your landing gear when you run. They keep you from wobbling or swaying out of control. 

When you start to roll your ankle, the peroneal tendons pull your foot back under you. 

If you ignore irritation and aggravation of those tendons, they can get weaker, tear or split apart. 

The sudden trauma of suddenly rolling your ankle can cause them to split as well.