Most can agree that in the spirit of the game both should have been reds. Both of them bust case because of the subjectivity written into the laws. I will highlight the subjective parts which lead to the refs officiating how they see fit.
SERIOUS FOUL PLAY
A tackle or challenge that endangers the safety of an opponent or uses excessive force or brutality must be sanctioned as serious foul play.
Any player who lunges at an opponent in challenging for the ball from the front, from the side or from behind using one or both legs, with excessive force or endangers the safety of an opponent is guilty of serious foul play.
VIOLENT CONDUCT
Violent conduct is when a player uses or attempts to use excessive force or brutality against an opponent when not challenging for the ball, or against a team-mate, team official, match official, spectator or any other person, regardless of whether contact is made.
In addition, a player who, when not challenging for the ball, deliberately strikes an opponent or any other person on the head or face with the hand or arm, is guilty of violent conduct unless the force used was negligible.
So by the laws of the game, both are are yellows if the refs decide they are, which they did.
So what’s the solution? Is football just an inherently subjective sport? How do you codify the spirit of the game?
As someone that officiated once upon a time, a wise referee once told the class that the difference between football and most other sports is that context matters in football.
Like most professions, there is a big difference between learning the rulebook and actual officiating.
Allow me to share the wildest example that I’ve ever experienced personally.
I was assigned to referee a local derby match and the players were boys aged 14-18. A high school match here in the US. During the warmup, the visiting coach informed me that one of his players is accused of getting a player on the home team arrested over spring break. You’d be a fool to think that off field incident didn’t wildly change how I had to referee this match in order to prevent the players from getting hurt. What wouldn’t be a red card in other games is now a red card in this game because of the off field circumstances.