Divorce / family law is very far my area of expertise, either personally or professionally, but if you're a multimillionaire looking to play hardball in your divorce (maybe to reduce alimony payments, if any part of that determination hinges on infidelity, or maybe to put pressure on your spouse to accept a less favorable distribution of assets?), making -- and leaking -- such a discovery request involving a figure of some prominence (e.g., head football coach at a major college program) would be a good way to drag your spouse's name through the mud in the media, regardless of whether that person has any relevant info / evidence.
Remember that the husband is also seeking discovery from seven other people. Anything is possible: maybe Charlie hit it -- or maybe seeking a subpoena for Charlie is the husband's vehicle for drawing much greater public attention to all of the discovery that goes on in the case than would have otherwise been possible. We'll see.