It depends.   If he would be determined to be a professional gambler, it would go on a Schedule C, Other Expenses, as gambling losses (or technically I would describe as "buy-ins") that offset the gross 1099-reported income.  If not a professional, two options - if he itemizes, I'd report as gambling losses/buy ins on Schedule A.  This is cleanest and would match the gross 1099 IRS reporting.  if he doesn't itemize, this leaves you with reporting contrary to the gross 1099 that may result in CP2000 correspondence from IRS.  I would add an explanatory footnote/sub schedule to the Other Income line of 1040  showing the gross 1099 less his own buy in contributions.  If he is absolutely certain of this 1099 accounting, then I would go for it - and advise him it may get scrutinized and to keep good documentation of it, then you fight it in a CP2000 correspondence audit if necessary.  Good luck, Eric J