Back both sides, across two books.

When two books disagree by more than their combined margin, backing both sides returns the same profit whichever way the game lands. No model and no fair-price estimate is involved — just two live prices and arithmetic you can re-check on two websites. Prices move in minutes: check both before placing either leg.

Both legs must land for the return to hold — if one leg is rejected or the price has moved, you are left with an unhedged bet. Sportsbooks limit and close accounts that do this consistently.