Is it possible to chat with people on my friendlist while I am playing a match? If so: how? I did not find any window or button for this yet.
You can type
The /r method will automatically fill in the username of the friend you are having the conversation with when you start typing the message. (It fills it in with the last user that messaged you)
They have to be on your friend list as well as in the same region as you for this to work.
If you have a friend that thinks it is fun to spam you during a match, you can use