Why is half of my "game" tab completely grayed out?

For some reason half of my “Game” tab is grayed out.
It appears this way in game, and does not change when I alter the resolution.

What is happening?


I guess you have changed Viewport Rect of your game camera. If you only need to show 1 game camera at a time then most likely you want it to be X=0, Y=0, W=1, H=1.