TMZ has learned ... San Francisco Mayor Gavin Newsom (right) and the mayor of Arlington, TX, Robert Cluck (left), have agreed to make a wager on the series.
Here's the deal -- each mayor has agreed that the loser will provide a day of community service in the winner's town while wearing a jersey of the winning team.
But there's more -- the losing mayor will also ship the winning mayor a bunch of delicious hometown goodies. If SF loses, Newsom has agreed to ship Dungeness crab, sourdough bread, Ghirardelli chocolate and Anchor Steam beer.
If Texas loses, Cluck has agreed to ship over BBQ food from a local joint called Spring Creek BBQ ... said to be the best in TX.
Game 1 is set for tomorrow night.