-a public school forcing or coercing children to participate in prayer,
that's just your accusation. As you said, You don't know this coach nor his intentions. You're just assigning the "forcing or coercing" on him.
And as I said, students can be victims of marginalization worse than this.
How about the same coach who also teaches social studies but hates boys who go out for cross country and makes their life hell up to and including giving out worse grades?
THAT goes on 50 fold in schools more than this concern over a choice to not participate in a prayer.