Enter losses as a "miscellaneous deduction" on Schedule A. You can deduct a loss only up to the amount of the win you report in the same year.
FORBES: Busted
2.
If you win, you probably also lose sometimes, and you can claim gambling losses as a miscellaneous deduction, up to the amount of your winnings -- but only if you have proof of the loss.
FORBES: Better buy yourself another filing cabinet