Screen would not unlock

Had a game as Bard where my screen would not unlock. A red box came around the league screen and sometimes if i clicked near the red box it would basically alt tab me from game.

I have no 3rd party screen recording or anything so not sure what it was. I had to restart finally because of course how do you play or even ult if you cannot unlock the screen.

It was normal after restart but I had to first abandon my team to restart.