Coaches are often hired as coaches, but their salaries are not justified that way. They are hired as "teachers", so that when the football/basketball/hopscotch season is over, they can continue in the employ of the school that hired them.

Teach math? No, don't know enough math to do the problems on the board. Teach science? And blow up the lab?? Nooooo. Teach English? Well, some do, but many aren't that well acquainted with literature either. Teach history? Sure! You don't really have to know much about history!

This, at least, has been what I have observed in the schools with which I'm acquainted. There are, to be sure, other history teachers who have specialized in history as part of their training. Those people would be the department heads.

The only decent history teacher who is also a coach that I know personally is a varsity soccer coach from England. He is a naturalized citizen of the US and has had to study American history to pass his citizenship test. He developed a passion for it, and is not only a very good history teacher -- think "concepts and trends with trivia for interest" -- but is the best civics teacher I have ever, ever met. He also had a grounding in non-American history from his English school, which gives him perspective.

If there's no passion, there's no excitement. If there's no excitement from the teacher's podium, then the subject will be a bore.