I believe, as another poster said, unless there is physical or emotional abuse, or an injury, a parent should not talk to the coach. I see no reason, however, that a player should not be able to talk to the coach man to man in a respectful manner from time to time.
My son went to the coach and asked for a chance and the coach said "why? do you think youre a better player?" My son wouldn't fall in the trap and said "I just want a chance." Idk if there was any connection but 3 days later he was promoted to varsity.
I had considered shooting off an email to the coach but in hindsight am so glad that I didn't. In high school it's time that young men learn to handle their business in my opinion, with guidance from the parent when needed/requested.