Seeking Opinions: Use of Non-Profit Lease for For-Profit Business

Does the following seem like a non-profit violation? If yes, does the violation create exposure for the non-profit status of the organization and the general board members?

A non-profit basketball league is leasing a gym for the exclusive use of the non-profit youth league. As part of the lease agreement, all maintenance is the responsibility of the non-profit. However, the executive board leader is permitting a friend to use the gym to provide private, for-profit lessons, for the friend's private gain. The friend is not contracted to provide services to the league at-large that would serve the entire league, and the non-profit board has not voted to approve use of the leased property for private training. The non-profit is not receiving any compensation from the trainer for gym time. The non-profit is not reporting any unrelated business income on the financials or the 990. Also, the private lessons are sometimes interfering with non-profit activities. This activity has been going on for over a year.

The market value of the gym time over the course of a year is approximately $15K to $25K. Further, it's unlikely the trainer is claiming the benefit of free gym use as income. Would the trainer's potential violation create exposure for the non-profit and/or board?

Any publications or case law that can be cited would be appreciated.