I'd say about 50-60% of the time when I start up a match in LoL my cursor gets locked into a tiny box in the bottom right corner of the game.
this is ingame on summoners rift, and I'm not the only person who has this problem. Sevral friends of mine have the problem of getting their cursor confined to about 1/4 the size of the games region in the bottom right corner. For some alt tab fixes it for others they have to QUIT the game and restart it to fix is (for my friend this means she's not back into game until about 3 min, because her comp loads slooooow)

Very annoying, putting that out there, hope you guys know about it.

bump

This happens to me very often, have you and your friends tried using Ctrl + Esc to minimize the window and reopen it (without clearing it)? It always fixes for me.

This happens to me as well- often after using alt + tab to go to another window during the loading. If you press esc during this time, it brings up the options menu and your cursor can move freely. However, clicking anywhere during this time minimizes the client. Doing that is my fix for it, most often.

I know all the fixes, thanks guys, it's just it's an annoying problem either way.
also my friends and I don't even need to alt tab to get it!

bumpity

bamp, red just say something for me, a simple period lets me know you've at least seen it.