Can there be/ is there a voluntary way to chat restrict yourself?

Right now as I type, my little brother is playing league. I'm not going to give a name or a username, but my brother is one of the most toxic players I've ever played with. He rages at his team mates, slams the keyboard, screams at the screen, and is basically a 13 year old terror.

Is there any way I can disable chat on his account?