So yesterday I was trying to get on League of Legends, but I noticed that the client just wouldn’t open. I was checking online for support or like 30 minutes until i found out it was Avast causing all the problems. I had to go into the Virus Chest and delete the game from the Virus Chest. Please add the game as an exception in your future updates, because now I keep feeling like Avast interferes with the game, which could be slowing it down or causing lag. Other Anti-Virus companies like McAfee and Norton by Symantec have already added League of Legends as an exception. I’ve been an Avast user for almost 5 years, and this is the first major problem I’ve stumbled across. So please fix this as soon as possible. Thanks. 
Report false positive >> https://forum.avast.com/index.php?topic=14433.msg1289438#msg1289438
Check out the viruses and worms sub-forum where this has been reported and passed up to avast.
There is also another here - https://forum.avast.com/index.php?topic=182960.0.