To everyone coming in and posting:
"I got banned, I don't know what I did wrong, I didn't get a message why" - It's something you either said, or did, in matchmaking that triggered either a report against you, or a flag for the enforcement team to look at you.
If you want to know what you did, or if it was in error, the forums here will not likely give you a personalized response.
Your best best is to submit a support ticket here: https://support.halowaypoint.com/hc/en-us.
Hopefully this process sheds some light for some of you on your behaviors, and how to correct them - or if you were indeed wrongly banned, it will help get it resolved.
I just don't understand why they haven't implemented a ban system that tells you, why you're banned. I haven't been banned personally (except when I do have to quit a game), but I can imagine it being pretty frustrating to get on, start playing, and just be told "ur baned lolz" without a reason. Wouldn't it make more sense so they know to correct that behavior?
The rules are posted in various places, and the support site is available to submit tickets and requests.
Perhaps it'd be nice to get a personalized message explaining why you get banned, but I don't think they're interested in hand-holding.
The support site is more than Bungie ever did for engagement with the Halo community, so I think it's a step in the right direction.
Perhaps there is a way to implement some kind of message in the future, but right now it might be tough. They may not have permission to email people, or send direct Xbox Live messages to people either. And if people have never been on Waypoint before, they can't send them a message here either. So it would probably need to be something in-game, and I think that's a lot trickier to implement than we might think.
That said, I think the support site is a good step for now.
[edit]perhaps the answer is to change the in-game message that says "you're banned until x/x/x" to also say - "Visit the Halo Support site for Information on how to submit a support request"
Although, this would probably open the floodgates for a TON of work to respond to things.