[splonk]

Depending on whether you're filing as a professional or not, you may be paying self-employment tax. But in general, gambling winnings of that nature (big tournament scores) are pretty likely to put you in a high tax bracket and/or trigger AMT. You can deduct losses but it's a bit of a fight with the IRS every year, since they have records of every time you've won $1200 or more, but no records of every time you've lost $10k entering a tournament and not cashing.

[baking]

If you fail to keep a receipt for a $10k entry fee I think that's on you.

Edit: I think you can't carry over losses from prior years, so if you lose money one year and make money the next, your taxes on your net earnings can be higher. Rule of thumb for professional poker players: If you don't have a profitable tax year, it is time to quit.