I would put in on Sch C or Sch C-EZ. It is income from work. Just like if he worked at McDonald's for a week or a month, never worked there before, and never will again. He would not get a refund of SS/MC tax. We never think anything about short stints with employers; I don't think we should with subcontractors working, either. I think the spirit of the law, so to speak, for line 21 is really "other" income, like awards, cancellation of debt, etc. You know, where there was no work.