See https://www.irs.gov/newsroom/know-the-difference-between-a-hobby-and-a-business
and
https://www.irs.gov/pub/irs-news/fs-08-23.pdf
An activity is presumed for profit if it makes a profit in at least three of the last five tax years, including the current year (or at least two of the last seven years for activities that consist primarily of breeding, showing, training or racing horses).
