I saw a live report from WDW on Fox News on my lunch hour today. They said that the latest accident happened in an acrobatic move when two CMs run and dive head-first at each other, pass one another, and then do a "tuck roll" landing on a mat. They said that the injured CM did land on the mat as planned, but it appears that his head hit wrong and he likely severally injured his neck. I'm guessing that it was something like the move the "bad guy" makes over Indy at the 4:32 mark in this video
I am actually still here at WDW and did not know about it until today when I went to DHS and saw that the show was closed. It's so very sad and my thoughts are with his family.