Pregame betting line movements
CRAZY NBA FACTS FROM THE LAST 14 SEASONS!!!
This 6-article series presents some crazy and interesting findings from all NBA games over the last 14 seasons (from 2002/2003 to 2015/2016).
Today we answer question #1:
Over the past 14 NBA seasons, does it seem like pregame betting line movements have an effect on which team is going to win the game?
The short answer to this question is: maybe… but if there is an effect, it appears to be relatively small.
We scrutinized all games from the past 14 NBA seasons for which we had data on the opening/closing betting lines. By opening line we mean the very 1st line published by Las Vegas sportsbooks. By closing line we mean the one just prior to the start of the game.
A fictitious bet was then placed on the team in favor of which the line moved during the day. For example, assume the opening line has Team A favored to win the game by 5.5 points over Team B. If the closing line went higher, for instance 6.5, we would make a virtual bet on Team A. On the other hand, if the closing line went lower, for instance 5.0, we would bet on Team B.
Most of the time, Las Vegas lines move according to the amount of money wagered on each team. If, for example, 80% of the money is placed on Team A versus only 20% on Team B, the line is subject to move in favor of Team A. The bookmaker’s goal is to entice gamblers to bet on Team B to balance things out. Therefore, the strategy described earlier consists of siding with the team on which most money was put on (generally speaking).
Let’s have a look at the results, where the first column indicates how much the line moved (absolute value of closing line – opening line):
Difference between |
Betting on the team in favor of which the line moved |
|||
closing & opening lines |
Bets won |
Bets lost |
Ties |
Win % |
0.5 |
1631 |
1673 |
38 |
49,4% |
1 |
1131 |
1159 |
47 |
49,4% |
1.5 |
664 |
669 |
12 |
49,8% |
2 |
324 |
347 |
10 |
48,3% |
2.5 |
229 |
210 |
6 |
52,2% |
3 |
122 |
124 |
6 |
49,6% |
3.5 |
49 |
65 |
2 |
43,0% |
4 |
37 |
52 |
2 |
41,6% |
4.5 |
29 |
24 |
1 |
54,7% |
5 |
12 |
19 |
1 |
38,7% |
5.5 |
9 |
6 |
0 |
60,0% |
6 |
10 |
6 |
0 |
62,5% |
6.5 |
7 |
7 |
0 |
50,0% |
7 |
5 |
4 |
0 |
55,6% |
7.5 |
5 |
2 |
0 |
71,4% |
8+ |
20 |
16 |
2 |
55,6% |
TOTAL |
4284 |
4383 |
127 |
49,4% |
A person following the strategy described above would have won 4284 bets, lost 4383 and tied 127, which is good for a 49.4% win percentage. In other words, doing the opposite strategy would have generated a 50.6% win percentage. That is not enough to overcome the bookmaker’s vigorish (i.e. the percentage deducted from a gambler’s winnings as a form of commission).
We have highlighted in red the win percentages that were below 50%. It is pretty interesting to note that they all occur in the upper portion of the table, which suggests following the plan below:
- For smaller differences (4 or less) between opening and closing lines: bet AGAINST the team in favor of which the line moved;
- For bigger differences (5.5 or more) between opening and closing lines: bet ON the team in favor of which the line moved.
Over the past 14 NBA seasons, portion 1) of the plan above would have generated 4299 winnings bets, 4187 losing bets and 123 tied ones (win % = 50.7%). As for portion 2): 56 wins, 41 losses and 2 ties (win % = 57.7%).
A word of wisdom: avoid putting this plan into action. Portion 1)’s win percentage is not enough to overcome all of the fees, while portion 2)’s sample size is way too small to advocate putting any money on this strategy. But it’s still interesting to see the pattern that occurred here, and you could incorporate this knowledge into your betting strategy.
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Thanks a lot for reading! Here is what’s coming up in next articles:
Over the past 14 NBA seasons,
- …has league parity increased or decreased? (you will discover strong evidence of league parity taking a SERIOUS hit over the last few years)
- …is there evidence of game momentum? (you will learn that, unlike popular belief, there is no such thing as “having the momentum” during a game. In fact, it seems like when a team goes on a roll throughout a quarter, it tends to strike back for the rest of the game. Like a wake-up call to their opponents!)