Your situation is not unique, I have seen it on here before as well as heard about it from other players.
You have several options, first one is to talk the coach one on one, no one else around, man to man and be honest and civil with him and ask him to be honest with you.
Sometimes there are personality conflicts or maybe you said something about the team or coach to someone who ratted you out, or maybe you did not say anything and your non-verbal actions did the talking for you.
There are 9 starters, not everyone can start. As long as you hustle, do the best you can do, and keep a positive attitude you will know you have done your part and hopefully the coach will notice. It's getting late in the HS season, so I don't know if it will work out for you this year or not.
There are a lot of unknowns, like what does the other players think about you?, what did you do last year and the year before?, how do you conduct yourself at practice and in games? Can you play ? How long has the coach been there, what's his record ? There are just a lot of varibles.
Good luck and never give up, just work harder and put a smile on.
CV