Runline betting in baseball is similar to betting against the pointspread in sports like football or basketball. The favorite on the runline will most often be -1.5, meaning it must win by more than 1.5 runs, and the underdog is usually +1.5, meaning it must lose by no more than 1.5 runs.
vig/juice on the runline favorite (-1.5 runs) is always plus-money
because the odds of that team winning by two or more runs are slimmer,
while the runline underdog (+1.5) is always minus-money because the odds
of them losing by less than two is greater.
For example, Team A is -1.5 on the runline with vig/juice of +140, against Team B at +1.5 on the runline with vig/juice of -160. That means for every dollar wagered on Team A -1.5 (+140), you can win $1.40. A runline wager on Team B +1.5 (-160) would require a bet of $1.60 for every dollar you want to win.