On this side, I referee sports and want to know if this is considered "qualified business income"

[DanielV01]

It depends.  It can be Qualified Business Income if you are in the business of refereeing: in other words; it is not a hobby, nor are you a volunteer nor and employee getting paid reported on a W2.  If you are a contracted referee, eligible to claim business deductions on Schedule C, this is income that can qualify for the Section 199A deduction.

The deduction calculation itself can be quite complicated, so even if you do qualify for the deduction, you may not realize a deduction of 20% of that business' income.  But you could well qualify for the deduction as long as your refereee is not hobby income, volunteer work, or performed as an employee.