Professional sports is big business in the United States. Total revenue across the four major team sport organizations — the MLB, NHL, NBA, and NFL — topped $30 billion in 2015.

Revenue in professional sports comes from a range of channels. While endorsements, advertising, TV deals, and merchandising all factor into team revenue, ticket sales remain important, as both a source of revenue, as well as a gauge of fan loyalty.

Year over year ticket sale changes for a given team are subject to a range of factors. 24/7 Wall St. reviewed 10-year changes in average home game attendance for professional hockey, baseball, basketball, and football teams across North America to identify the teams that are losing the most fans. For 17 teams, average home game attendance declined by more than 10% over the past decade.

Click here to see the sports teams running out of fans.
Click here to read our detailed findings and methodology.