If you're shooting a firearm, you can shoot quartering away, broadside, quartering toward, and directly toward. All of those are legitimate and ethical shots. Just imagine a line from where you aim to where it would exit and make sure that line passes through the vitals.

I've heard of people saying that shooting straight up the rear of a deer will bring it down from massive bleeding but it's a guaranteed gut shot not to mention a slower kill and almost universally considered unethical. (Don't do it!)