A backroll is Mexican when instead of turning your head towards your lead shoulder and throwing it out and away, you tuck your head down and throw it like an inward front flip. Think of two posible axis on to which you can throw a backroll. On a regular backroll, you rotate on an axis that runs through the front of your body to the back like a cartwheel. On a mexican backroll, you rotate on an axis that runs through your lead hip to your back hip. Hope this helps!