This is a weird one....because the 'victim' has himself completely missed the ball as well. The fouling player, seems like he was making a black based on expecting the opponent to actually connect with the ball.
Sure, studs up onto a player's follow-through is very dangerous, and had the player kicked the ball and then been caught by studs like this it's an easy red.
But given that the 'victim' had no right or reason to be doing a wild airswing himself, I just don't know if I can say there's enough culpability for a red card.....though there's some risk.
A caution seems appropriate for me, and dfk. The 'victim' just has to share responsibility here. I'm not sending off a player because an opponent decided to kick his studs.
invent? Intent isn't required for a RC. It can be a useful measure but certainly not required.