It’s an “over reach” injury if he stepped on himself, meaning his rt hind hoof reached under himself too far as his right leg came back and the two met. I saw the photo of Matterhorn apparently stepping on or towards him out of the gate - hard to tell. Either way, the injury is in an area called the hoof bulb which is a sensitive area of their feet and no doubt, cost him the race. Imagine, if this horse was injured coming out of the gate and in that much pain, he went on to run 1.5 miles on it and finish in a photo for 4th place - as he was walked off the track you could see he was “toe-pointing” lame on his rt front - amazing heart these horses have!!
I love this horse. He really is a champion, even if his owner acts like a d!ck sometimes.
Get well soon, Chrome. You still have some great races in you.