I'm not going to play next year if coach makes me ride the pine again this season. (source)
The sentence syntactically suggests "coach" has to be a proper noun, although it is not capitalized. It looks to me "coach" here functions the same way as "Mom" in "I asked Mom where my book was."
Should it be capitalized when used as title before a name? For example:
Have you talked to Coach/coach Anderson?
A discussion on a sports journalism forum on this topic has mixed opinions and seems ultimately inconclusive, so I wonder what the proper writing rules are.