A run line bet is a bet type that refers to the number of runs a team must either win by or lose by in order for you to win your bet. For example, if a favorite is favored to win by 2 or more runs their run line odd would be -1.5 and they must win by 2 or more. In this example, if a team is an underdog their run line would be +1.5, which means they can lose by 1 run or win outright and you would win your run line bet.