I've slowed it down frame by frame, and to be honest I think it was a total accident. Coutts is shaping to shoot, and Sordell is looking over his shoulder to see the ball, then raises his foot to try and kick it. Coutts gets the shot away, and the momentum of his shooting leg means he kicks into Sordell's outstretched (and straight) leg.
There's still an argument for a red card, as it clearly can't be argued that it endangered an opponent - the straight leg that I referred to is why I think a red can be justified. I'm much less sure about excessive force, and I think most players would have done the same in trying to block the shot. That's why I think it was a freak accident more than anything else. I've seen broken feet from kicking into an outstretched leg, but I don't ever recall seeing a player break his leg in that way. Also, when an injury like that happens you normally see team mates racing after the player who has caused it, but there doesn't seem to be any of that here.
Hopefully he makes a full recovery.