Hello there, I'm not very sporty, so someone may contradict me . . . :-) To me, both 'coach' and 'instructor' are fine. You talk about a football coach - that can be both a professional career, or a part-time voluntary activity. I have found an Internet site which defines instructor as someone who teaches a specific set of skills, while a coach develops the person in a wider sense. But for your situation I would say both would be quite correct.

The traditional word would be "instructor" but "coach" is more and more common and trendy. You could call yourself a coach if you wanted. If you get the feeling that your potential clients would be more impressed with the word "coach", then you could use it. Essentially, it's a marketing choice.