lol....so funny that you're actually worried about this meaningless threat.
Now, a number of people have said that it's impossible to get your IP from League. This may not strictly speaking, be true. It is true that your IP information would be logged on Riot's servers and hacking them would be the only way to get that information from the server. However, it may be possible to get IP information from live games. It only depends on how Riot implements it's network protocols. In older online games like StarCraft BroodWar, the Battle.Net server is only a hub where players can meet and join up in games. But when the game starts, the game connects players to each other and maintains a connection to the server. If Riot implemented their protocol this way, it would be possible for someone to monitor their TCP connections and UDP transmissions made by the game. They would be able to get all the TCP/IP end points of which some will be the other players' IP addresses.
That being said, such threats are still meaningless. For one thing, the average internet user has a dynamic IP which is assigned by the ISP. It is entirely possible for you to have one IP today and another tomorrow. While there is some organization behind how IP addresses are distributed, the best someone can do is a rough estimate of where you live. You can easily find the country where they live but anymore than that would take some effort and it will depend on the ISP but the average person will not be able to trace an IP address to an exact location. The only exception is if they are an extremely powerful individual like a judge or government official with the power to force the ISP to give up your location. Or they could be a privileged employee of the ISP that provides your internet and has access to that information. Both scenarios are highly unlikely. I think judges have better things to do than complain about feeders in an online game.
One final thing. Let say they do get a list of IP addresses the game has made connections to, they would have no way of knowing which connection is yours. They would have a list of 9+ connections. 9 for the other players, yourself included and a couple other connections, usually to the server for the purpose of housekeeping during gameplay. And of course, everything I said is moot if Riot didn't implement their protocol like old StarCraft's Battle.Net protocol. All this only works if it is implemented as such.