The sports book is obligated to report the gross winnings not the net winnings to the IRS.
So the W2G you receive from the sports book cannot be for the net amount.
In order to claim gambling losses, you have to deduct losses as itemized deductions (which the sports book can provide you).
You are limited to claiming losses up to the amount of gambling winnings you are reporting on your return.
Sports Betting Taxes Guide
