Sim football works when a bad rep gets corrected instead of argued about. The league office exists for exactly that: you saw something in a game that broke a rule, and you want it ruled on.
You have a case when you have three things — a specific play, a specific rule, and a clip. Missing one of those, you don't have a case yet.
Take it to the other coach first. Most of what reaches the office is a misunderstanding two adults could have settled in five minutes.
Posting in league chat is not filing. Venting there does not start a case. If it matters enough to be ruled on, put it in front of the office.
The standard the office rules by is Playing in Good Faith in Gameplay & Settings. This section is how you bring it a case.