In the universe of the "John Wick" movies, there's several hotels accross the world, called "The Continental". These hotels, which are mainly (if not exclusively) for hitmen, have several set of rules, including but not limited to:
- Carrying out a contract within the building.
- Fighting or killing someone else within the building.
In the first movie, these rules are the reasons why Ms. Perkins' membership was revoked and her life was forfeited, since she killed someone within the building.
In the second movie, these same rules are the reasons:
- John and Cassian stopped fighting when they rammed through a Continental window during their brawling.
- John got his membership revoked from killing someone.
However, during the first movie, after John told Charon over the phone that he was "dealing with an uninvited guest", the latter asked him whether or not he'd need "a dinner reservation" (hinting to the possibility of killing Ms. Perkins).
Considering that the rules prohibit killing in any way within the hotel, doesn't it mean that Charon would have taken a dinner reservation for 2, had John killed Ms. Perkins?
This question is related to this one. However, the other answer claims that self-defense doesn't count as killing. That doesn't explain why both John and Cassian stopped fighting. John was in a position of self-defense, which, according to the other answer, doesn't break the rules.