With sports gambling recently legalized and left up to the states and our readership’s general proximity to both New Jersey, Delaware, and the internet, I figured we could do a quick look at the Atlantic Division’s recent performances against the Vegas spreads. First though, a quick primer on how spreads work. Skip if you know this already.
Example Spread #1
In this situation, the Sixers are -10 (minus ten), indicating that they are favored to win this game by 10 points. You can place a bet on the Sixers, but you would win only if the margin of victory by the Sixers was greater than 10, 110 (PHI) - 99 (DAL) for example. If you placed a bet on the Mavericks to cover the spread, that means you believe the Mavericks will lose by less than ten points (this includes winning outright), so you would win your bet if the score was 110 (PHI) - 101 (DAL). If the margin of victory was exactly ten, you would push the bet.
Example Spread #2
Philadelphia 76ers (+9.5) vs. Golden State Warriors
The plus sign before the number now indicates that the Sixers are nine and a half point underdogs, and that they cover the spread if the lose by less than nine. 100 (PHI) - 109 (GSW) would result in the Sixers covering, whereas 100 (PHI) - 110 (GSW) would not. More information here.
I took all the regular season spreads and outcomes from 2015-2016 through 2017-2018 (via www.covers.com) for the Atlantic Division and threw them together. Figure 1 is a histogram by team of the spreads.
Unsurprisingly, the Celtics and Raptors were heavily represented in the -# side of the spreads, and the Knicks and Nets being fairly strongly weighted towards the +# side. The Sixers are still predominantly underdogs due to including 2015 and 2016 seasons. Fun fact, these colors are the NBA sanctioned hex codes for the team colors, and they look super gross together.
Percentage of Games Covered
Now, what we really care about though is how the teams performed against the spread. That is often a good judge of whether a team over or under performs according to Vegas, and Vegas is pretty much the best arbiter of quality. Figure 2 shows how often each team covered based on a particular spread.
You will note that the graphs jump all over the place. Due to the high number of possible spreads, it is easy to go 0/1 or 1/1 on a discrete spread and graphs display a high degree of movement. Vegas sets the spreads to get equal action on either side, so keep that in mind as well.
Percentage of Games Won
Since this is technically a sport and we theoretically care about winning the games and not just covering the spreads, Figure 3 is a look at the percentage of games won by spread.
Again, it makes sense to see a decreasing trend from left to right. The higher a team is favored to win by, the more likely they are to actually win, regardless of the margin. The opposite is true for games they are not favored in. Of note, once the spread is about -12.5 or greater, the percentage of wins seems to be pretty small.
This was just an extremely cursory look into gambling, but if this topic is something that you would be interested in seeing more of, let me know in the comments below.