I'm not going to argue too hard, as my overall stance of "if you genuinely think it's SFP then fine" does apply. But I can't get on board with the idea of any trip, even a surprise trip, escalating to the point where it deserves the same punishment or reaches the same level of danger as a straight-legged off-the ground lunge. SFP red cards are typically for tackles that either impact hard with a vulnerable part of the opponent's body, or risk doing so.It is dangerous though. And I can't think what other challenges we would have to grade the same.
As I said earlier, if you take the Xhaka example. And the Joe Ralls example and find those threads you will find me vehemently opposing red cards.
The difference for me is that both the Joe Ralls and the Xhaka ones the foul is made from the front of the player or reaching around so they have the opportunity to take defensive action to break the fall. This is just a straight up kicks at the players ankle and the first he knows about it is the taste of mud
Having been the victim of someone just kicking my legs from behind (albeit playing rugby with "friends") I can tell you my safety was endangered by that action. It bloody well hurt for weeks after. It's the surprise element the body can't react quick enough and you just smash the floor with whatever part hits the ground first.
I've never once before seen the impact with the ground cited as a reason for going red, you're breaking new ground here! But I just think it opens up too many potential reds - player looking for a high ball getting barged in the back by surprise and falling to the ground for example. Typically that would be a foul and get on with it, but it meets your criteria for red.
There was a lot of chat last year about Kane's habit of undercutting a player jumping for the ball, which often resulted in the opponent landing on their head or neck. And even in those examples which are considerably more dangerous than a player falling on their front from standing, the question was generally "Who should get the FK" rather than "is Kane lucky not to see red?" I just don't see SFP red here as remotely in line with any other SFP in the history of the game.
Again, by all means I'd love to see a specific red card offence created for "stopping a promising attack with no chance of touching the ball", but I don't see how these qualify as SFP without the player getting the challenge seriously wrong (the Bolton example posted above being a good example of this).