So I am just guessing here, but I think Horn's cleat got tangled in the turf and when he went to push off and "explode" into the play that's where he broke the bones. He's a pro athlete and his leg muscles are probably off the chart strong....he started to get into the play the cleat held his foot in place and him being so strong probably fractured his metatarsals. I am going to guess the three laterally which means one could be a Jones Fracture (which I had and sucks balls when you have to let it heal by itself without surgery....think like 5 months non-weight bearing).
Really sucks for Jaycee and the Panthers. Let him heal up and don't even think about rushing him back.
Also, turf sucks but I also have to wonder if there are shorter stubbed cleats these guys could be wearing to help prevent this kind of thing. I am guessing the answer is no.