Yeah I just found this in the explanations:
Points Spreads
The Points Spreads maybe be confusing at first. You might see an event such as:
Chicago -3
Atlanta +3
This would indicate that, once the result of the game is in, you either add three points to Atlanta's score or subtract 3 from Chicago's score to get the winner of the bet.
So, say the result of the game was Chicago 20 - 18 Atlanta, then, while Chicago won the game itself, they only won by 2 points and so Atlanta would win the bet.
In the event of a tie, all bets are returned. Taking the above example again, if the game result had been Chicago 20 - Atlanta 17 then adjusting for the spread makes them equal. This is called a "Push" and all bets are returned.
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And I feel like an idiot for not knowing before.....