Key Numbers

Last week, I introduced the terms public money and sharp money and went over in detail the reasoning behind the line moves for the first round of NFL playoff games. This week I wanted to talk about key numbers and the NFL was kind enough to provide a couple of textbook cases. Based on the large number of emails I’ve received on the topic, it seems that even moderately experienced sports bettors don’t understand this concept and hopefully I can shed some light. I want to thank Bodog’s head bookmaker Kent for his insight into this topic and for providing me with such detailed information about the line movements this past week.

Before getting into details of the games themselves from this past weekend, I need to explain the concept of key numbers in a little bit of detail. First off, football is unique among the major pro sports in terms of how points are scored. In baseball, hockey and soccer, all scores are valued as a single point. These sports also tend to have low scores and the average margin of victory is extremely low so pointspreads aren’t used in the same way as they are in football and basketball, and moneylines are the most common form of betting. Basketball scores come in increments of 1, 2 or 3, but the high amount of scoring makes for an even distribution of final scores. As a result, basketball is perhaps the simplest sport to wager on in terms of lines offered. Football gets complicated because the scoring comes in chunks of 3 points (for a Field Goal) and 7 points (for a converted Touchdown). There is also a small amount of other scoring possibilities with safeties providing 2 points, missed extra points making a Touchdown worth only 6 and the two point conversion making 8 a possibility. Scoring in football tends to take place in football on average only about 8 times a game so, unlike basketball, the final scores do group around certain numbers, known as key numbers. The major key numbers are 3 and 7, but 1, 4, 6, 10, 13 and 14 have a high likelihood of being the final margin of victory as well and are sometimes referred to as minor key numbers. If we look at how all these numbers relate to 3 and 7, its easy to see why they occur frequently. The following chart shows the frequency of certain final scores for the 2001 NFL season as well as the relationship of the number to a combination of Touchdowns and Field Goals:

  • 17.3% Field Goal
  • 7 9.7% Touchdown
  • 10 6.9% Touchdown + Field Goal
  • 4 5.6% Touchdown – Field Goal
  • 1 4.4% Touchdown – 2 Field Goals
  • 6 4.4% 2 Field Goals
  • 14 4.4% 2 Touchdowns
  • 13 4.0% Touchdown + 2 Field Goals

It is easy to see that a Field Goal was the difference in a lot of NFL games this year. I’m sure that this is not a big surprise to you but lets look at this from a sportsbook’s point of view. Lets use the real world case of the Oakland-New England game this past weekend to illustrate the danger to the House and what sportsbooks must to do to avoid the peril. The line in this case opened with New England -3 and action came on the Raiders. As mentioned in previous issues, the House is always seeking to balance action and minimize risk, so in this case Kent wanted to move to the Patriots -2.5. Due to the high probability of the final score landing New England by 3, he chose not to do so. Lets look at some theory now to examine why he didn’t make that move.

In the most basic of cases, lets assume there were wagers of $110 to win $100 on the Raiders +3 and then $110 to win $100 on New England -2.5. The game is balanced but the House would risk being sided if the game ended with the Pats up 3. The Oakland wagers would be pushed but the Patriots wagers would be winners so the House would lose the $100. In this case, the House would be in a situation where it could only lose $100 or collect the vig ($10) if the score fell on any other number. If the house had stayed at -3 and remained exposed the $100 on Oakland, a Pats win by 3 would have resulted in a push, where as any other outcome would result in either a $100 loss or a $110 win for the House. Same worst case of a $100 loss, but now the upside is much, much better. This is why sportsbooks are very reluctant to move off of key numbers. The chance of the final score for a game landing on 3 is roughly 17%. Assuming an even split between dogs and favorites, the chance of a 3 point favorite winning by 3 is about 8.5%. This would mean that 8.5% of these games would result in the House being sided or middled. This would be disastrous for a business where 4.5% is the profit margin! It’s also worth noting that the same risk applies in moving onto key numbers. If money comes in on the favorites at -2.5 and the dog at +3, the House would be in the same situation if the score fell 3. Now lets look at what sportsbooks do to balance action without moving on or off key numbers.

There are two ways a sportsbook can avoid the risk of key numbers. The first way is to know what the closing line will be and to get to it as soon as possible. Unfortunately, this is very difficult to predict and mistakes can be costly. As an example this past week, Chicago opened as a 2-point favorite over the Eagles. Kent noted that early sharp action was on Chicago and he quickly moved to 2.5. Public money tends to come in on favorites, so it looked like both the public and the professionals would be on the Bears. This is why, after limited action on the Bears at -2.5, Kent moved to -3. He admitted there was some risk at moving from -2 all the way to -3, but as the move was very early in the week and the action still small, the risk was less than he stood to make in vig from being at -3. Action was fairly balanced at -3, but there was a little more on the Bears, so moving to -3 was the right call although the final score, Philly 33-19, made it a non-issue.

The other way to balance action is to alter the odds associated with the pointspread. Most pointspreads are offered at standard odds of -110, meaning you must risk $110 to win $100. (Remember that when sportsbooks move a pointspread, the odds don’t change, as the spreads only affects whether your wager is a winner or not. Changing the odds, on the other hand, doesn’t affect whether your wager is a winner or not, but instead affects the payout.) By changing the odds away from the standard of -110, the House can make the same line more or less attractive to people looking to place wagers. This past weekend’s Oakland-New England game is a good example. As mentioned above, the line opened with Patriots -3 and early sharp action was on Oakland. As public sentiment for the Patriots had been growing all season, Kent was reluctant to move off of 3, so he altered the odds to make wagering on the Raiders more expensive and wagering on the Patriots more attractive. His first step was to move to New England -3 (-105) meaning that wagers on the Pats now required a risk of only $105 to win $100 while wagers on the Raiders now required $115 to win $100. From there, Kent moved to -3 (Even) and -3 (+105) before bettors decided to take the value and bet New England. The downside to this method is that it reduces the vig collected by the house, but a smaller profit is better than a big loss. At game time, the action was close to balanced, with a slight lean to the Raiders and when New England kicked a Field Goal in Overtime to win by 3, Kent was quite relieved that he made the correct choice and stayed on 3.

Now when you see a sportsbook offer a line that is off-standard (other than -110 on both teams), you will know the logic behind it and hopefully you can benefit by looking for some value and laying less than -110 on the team you want. This also explains why many books charge premiums for buying points on or off key numbers.

Next week, I’ll take a look at Halftime Betting, the lines for the AFC and NFC Championship Games as well as take a peek ahead to the Super Bowl.

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Rob Gillespie is President of Bodog Sportsbook & Casino