A signed release (as we explain here) should serve two purposes: the subject consents to use of interview statements, and the subject releases you (and your publisher) from being sued for libel, invasion of privacy, or copyright infringement (since the speaker’s words may be copyrightable).
Player v. coach. There shouldn't be a substantive difference between a player's release and a coach's release except for the "parental consent" provision that you can use for players under the age of majority (18 in most states). We've posted a sample interview release at the Stanford Fair Use site that includes an optional "parental consent" provision. (We've written about parental consents here and here).
