Looking at the slow mo's It looked like he slipped just before he entered the ash/dirt
Very few would argue that Ruby is without peer, but he seems to ride with more determination and flair on this side of the Irish Sea than he does at times when riding at the gaffs in his home country. McCoy simply isn't the man he was five or six years ago in my opinion, although that still makes him a damn fine rider anyway.
I wasn't impressed by his jumping, neither Pasco's for that matter, both are meant to be exciting types, but I beg to differ at present.
The horse jumped the last perfectly well, than lost his front legs under him on the ash/dirt about 10yds after the last hurdle.