Didn't read through the entire thread, but my two cents:
Sat next to someone with massive amounts of expression in the activity last night. He told me that he noticed this person struggling from early on in the show. I did not see anything until right after the guy went down. So, I felt it was a pretty firm conclusion that he had either injured himself early on or gone in injured and pushed himself way beyond what could be expected.
This was, by far, the worst thing I have ever seen in drum corps. It ranks right up there with the most disturbing sports injuries I have seen on TV. And I have never seen anyone travel so far unassisted with so serious an injury. It is really tough to imagine how much pain this individual must have endured just pushing himself far enough to sustain the final injury, much less attempting to get off the field.
I join everyone else in just really hoping that he is able to recover completely from this.