The Colts are down 13 points and have the ball at their own 15-yard line.  There is just over three minutes left to make an unlikely comeback against the Patriots.  Andrew Luck uses eight straight shotgun passes to drive 85 yards and throw a touchdown to wideout Griff Whalen, making the score New England 34, Indianapolis 27.  After a blocked extra point and a failed onside kick, that would become the final score.

The betting line for that game opened at Colts +7 and closed at Colts +8.  For most bettors, that touchdown either flipped their winning bet to a losing one, or vice versa.  While many might see this touchdown as a random event, many others refer to a different mantra: Vegas Knows.

Any time a game ends with a spread close to the betting line, or ends on a crazy play, everyone claims that “Vegas” knew something that everyone else didn’t.  (Side note: people often incorrectly use the word Vegas when referring to online sportsbooks that take place in the Caribbean but the sentiment remains.)  A quick twitter search after one of these games will quickly reveal how many people believe in this idea.

But how much does “Vegas” actually know?  Let’s take a look at the past five seasons of NFL closing lines at Pinnacle against the actual results and see how accurate these lines are.

Including playoff games at the beginning of the 2010-11 season, there are 1494 games in the entire sample.  Over the entire sample, the average difference between the closing line and the actual result was 10.5 points.  That’s right, ten and a half points.  To be fair, blowouts can skew your results towards the higher numbers, so let’s take a look at all data points:

Excel Chart

And here are the percentage of games that fall within each data point:

1/2 point6.0%
1 point9.5%
2 points15.9%
3 points21.0%
4 points28.1%
5 points33.5%
6 points39.8%
7 points46.2%
8 points50.9%
9 points54.5%
10 points58.8%
14 points72.4%
17 points79.5%
21 points87.6%
24 points91.8%
28 points95.7%
35 points98.8%
42 points99.7%

What this chart shows is that 2.7% of games landed exactly on the closing line.  21.0% of all games were within 3 points of the closing line, with 46.2% of games within a touchdown.

While sportsbooks aren’t just throwing out bad lines, this shows that they don’t KNOW what’s going to happen any more than casinos know that the roulette wheel is going to come up red or black.  The advantage the books have is that they are charging you to bet.  The vigorish is the advantage that the sportsbooks have, not an innate ability to predict when touchdowns occur.  All sportsbooks are created with a house edge, and with that edge #VegasKnows that they can’t lose.