Under FINRA rules, which of the following activities is not considered an outside business activity (OBA)?

Selling real estate is considered an outside business activity because it involves actively engaging in a business that generates income outside the registered person's primary employment with a FINRA member firm. This activity requires licensing and is directly linked to the individual’s professional capabilities.

Selling health insurance also qualifies as an outside business activity since it entails actively working in an insurance capacity, requiring appropriate licensing and taking place outside the registered person's primary employment. This activity generates income and could potentially create conflicts of interest with their primary role.

Professionally refereeing athletic events is classified as an outside business activity because it involves active participation and income generation outside the registered person's primary work. This engagement requires specific skills and could pose potential conflicts with the individual’s responsibilities at their FINRA member firm.