As for that video; Jason Allen was the only one willing to get in front of Ronnie Brown.......and atleast Ronnie Brown went down (even if Jason Allen looked like a ragdoll).
If you notice.....
Ronnie Brown has a full head of steam, Allen has two choices...
A. Go for the big hit; try to get lower than Ronnie Brown. Let's say Allen does get lower than Ronnie Brown; in this situation there really is no guarantee he brings him down. There's a good chance Brown either dislocates your shoulder or just leaps over you (Bills game last year, where Brown leaped over a defender trying to get lower than him......Brown ended up scoring a TD). Bottom line: If you try to lay a big hit on Brown, try to blindside him or get him when he doesn't have a full head of steam (this applies to most 230+ pound running backs that run with power)
B. Stay your ground. Let the runner come to you and wrap up. It was a great effort by Ronnie Brown; he would've scored either way.