https://www.torproject.org/
lols
a) That's for browsers, not games.
b) Even if it was for games, enjoy your 1920ms ping. If you're lucky. Seriously, if you've used Tor for 5 minutes you realize it's barely tolerable for basic browsing. Games would be completely out of the question.
ANYway, things to watch out for with IP-based checks and bans:
* IP's which resolve to a .edu address, where lots of people will tend to have the same IP.
* IP's which resolve to something that looks like a business. I'm pretty sure I got an entire 20,000 person corporation banned from a particular, popular website. (They did not like my political views so they banned my IP, which I'm pretty sure the entire corporation used, or at least everyone on the east cost of the United States).
I imagine, though, that the IP match is only step 1.
Step 2 would be to put those accounts on some sort of watchlist. If they are both logged in and active, fine. If they tend to show up to empty servers at 4am on Tuesdays on opposite teams and reap 5x rewards with little or no action from one of the accounts then you can probably safely ban them both.
I don't really know what information is available to chadz though. I'm just saying that IP, by itself, has flaws when it comes to knowing how many warm bodies are involved. It's not a bad start, though, and multiple accounts could be a real problem if left unchecked.