How to get a global ban in minecraft?

I heard it takes 3 bans to get a global ban in minecraft but I don't know much about it, not sure if that's right. Can someone tell me about it?

I'm not aware of any "Global Bans" for Minecraft… But I'm aware that servers that are using the same Ban-logging add-on to their Bukkit server MAY have such a policy.

Server's using a Ban-logging add-on can check that service's database to see if a particular player was banned on other servers using that same service. If you get banned on a couple of servers utilizing this service, it can blacklist you on all other servers you haven't played played on yet.

In regards to the basic or "Vanilla" servers, there's really no ban logging service built into that… So you can get banned on multiple vanilla servers with minimal issues as those bans aren't getting reported to any centralized group.

Hope this helps!