And how do you know it was from sports betting?  Were you there with him?  Many of these casinos and online gaming outfits offer incentives, like "first bet matched even if you lose."  When all else fails, call the number on the 1099-MISC and ask them why it's not a W-2G.  They may tell you that they are following the instructions for Box 3:  "Also include amounts paid to a winner of a sweepstakes not involving a wager. If a wager is made, report the winnings on Form W-2G."