Cheifs/Browns Safety?
 

Watching this game, Green throws and interception in KC's endzone. The receiver tries to tackle him but misses. The player that intercepted the ball then stubbles out of the back of the endzone. Under what circumstances would this be called a safety? Just wondering.

With what you have described, never. He could run around forever in the EZ, break 5 tackles while in the EZ, then step out the back on his own and it would still be a touchback. The definitions of OOB's and what causes a TB will show you why I can say that. I would encourage you to look at those in the rule book for further understanding.

Canadian Ruling
 

No safety in Canada.

To get a safety call here the player intercepting the ball would need to bring the ball out of the end zone into the field of play and then go back into the end zone (i.e., he would be the one forcing the ball into the end zone) and then ... go OOB in the back of the end zone. The way you described the play the QB with his forward pass put the ball in the end zone and MJT's analysis is correct.

One thing that could cause this to be a safety in NCAA or FED would be a penalty in the EZ while all this running around is going on. Not positive if this is also true in NFL.

I always ask this question: "Who caused the ball to go into the EZ?" NOT the one who intercepted it.