MLB run line is a type of bet that you can place in a baseball game. It allows you to decide the winning favourite or losing underdog. The only difference in run line and money line bets is that you need to specify the winning (-) or losing (+) 1.5 runs here. So you win the wager on a favourite if they win by two runs. In case you place a bet on the underdog, they must win the game or lose by one run to make you win.