Re: Jack turns back his head and looks back. He realizes that Chad is getting closer.
The part in italics is very awkward.
Originally Posted by Nikitus
You could say "Jack turns his head and looks back." But you don't really need to say that - we don't have eyes in the back of our heads, so we must turn our heads. "Jack looked back and realized Chad was getting closer." (Your present tense: Jack looks back and realizes Chad is getting closer.)
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.