well now, there are a chitload of variables that need to be addressed.
If you have received a W-2G, you claim such winnings as other income on page one of Form 1040 and you deduct all losses up to your winnings as an itemized deduction of Schedule A.
If you want to say you gamble for a living, or as a professional, you can choose to file Schedule C and attach it to your 1040. On such form, you would claim all gambling revenues and deduct all expenses related to gambling activities (not just gambling losses). This treatment raises other issues and potential red flags. If you want to try and claim losses and actually reduce gross income, you may have to prove it's really a business and not a hobby. If you show net income, not only will you pay income taxes, you'll have to pay self employment taxes.
Claiming it as a business raises one more very important issue. Losses from illegal activities are not deductible, although income from illegal activities is taxable (it's good to be the government). If sports gambling is illegal in your state, you're fucked.