Because you see horse collar tackles regularly in football, or even the NFL or rugby? And there's no reason at all it's become an international meme? If it were a common thing there wouldn't be the uproar about it that there has been. Collaring someone can easily be seen as violent conduct.
"The horse-collar tackle is an American football maneuver in which a defender tackles another player by grabbing the back collar or the back-inside of an opponent's shoulder pads and pulling the ball carrier directly downward violently in order to pull his feet from underneath him. The technique is most closely associated with Pro Bowl safety Roy Williams.
After being blamed for a series of major injuries in the 2004 season, the horse-collar tackle was banned from the NFLduring the 2005 off-season. The rule forbidding it is often referred to in the press as "The Roy Williams Rule".[1] The rule, with modifications, was adopted in college football in 2008 and high school football in 2009."
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Risks[edit]
The horse-collar is particularly dangerous due to the awkward position of the player being tackled, who will often fall backward in a twisting motion with one or both legs trapped under the weight of his body. This is exacerbated if the player's foot gets caught in the turf and by the additional weight of the defender. Potential injuries include sprains or tears to ligaments in the knees and ankles (including the ACL and MCL), and fractures of the tibia and fibula.[3] Smith, for instance, was effectively sidelined for two seasons after a horse-collar tackle by Williams broke his right tibia.
The ban states that a horse-collar tackle is an open-field tackle in which a defender uses the shoulder pads or jersey to immediately bring a ball carrier down. The term "open field" means that horse-collar tackles committed near the line of scrimmage will be allowed."
If you think a 'tackle' that has a full wiki page and a breakdown of the potential damage it can cause is not potentially red-worthy then you either haven't considered the potential fallout from it, or you don't care to. Saka being left in a broken heap would've engendered a different response from some who found the foul to be amusing and 'just Chiellini, the lovable rogue'.
It's a very easy red for another ref. Antics like that should not be condoned or marked down to nothing serious.