The 2017 NFL season kicked off last night with a considerable upset, as the Kansas City Chiefs beat the defending champion New England Patriots 42-27 in Foxboro, MA. The Patriots entered the game as one of the week’s biggest favorites, laying eight points at game time.
The 23-point difference between the point spread and actual result is significant. Sure, it’s only one game, but could it be emblematic of a broader challenge that bookmakers and bettors face in Week 1, when they have to make decisions based on projections and personnel rather than performance? More specifically, are Week 1’s NFL betting lines generally less accurate than those of other weeks?
The idea doesn’t seem all that unreasonable. But alas, it isn’t so. In fact, contrary to what we might expect, Week 1 averaged the second-most accurate lines of the NFL’s 17-week season from 2012 through 2016. Put another way, the average absolute difference between Week 1’s point spreads and actual margins of victory is lower than that of every other week but one (Week 7).
Over the past five seasons, the typical Week 1 NFL betting line has been 8.64 points off the mark from the game’s actual result. The average difference across all 17 weeks was 10.25 points.
(Note: The Harvard Sports Analysis Collective ran a similar study and reached similar conclusions. They further noted that from 1985 to 2015, Week 1’s NFL lines were average in terms of accuracy.)
When we peel back the onion a little further, we uncover a couple of other interesting things about the NFL’s opening week. From 2012 to 2016, Week 1 averaged the lowest lines and 2nd-lowest margins of victory of the season. (Note: You can’t simply subtract one from the other to get the average difference because sometimes underdogs win outright, like Kansas City did last night.)
Our five-season sample is relatively small, but it appears that bookmakers’ and bettors’ lack of information about teams in Week 1 limits how high they’re willing to drive the lines. For their part, teams tend to keep their opening games close – maybe because they’re healthy and have extra time to prepare, or possibly because the NFL seems to prefer certain rivalries and rematches in Week 1.
Not surprisingly, Weeks 16 and 17 feature much higher betting lines than other weeks, as these final two weeks of the regular season can pit known good teams fighting for byes and playoff spots against known bad teams with nothing to play for. We can conversely speculate that the tighter-than-average lines in Weeks 12, 13, and 14 result from more teams battling for their playoff lives.
There is no solving Las Vegas, but at the very least week-by-week analyses like this enable us to scratch the itch of intrigue and shed a little light on the hidden quirks of NFL betting lines. Stay tuned for more fun looks throughout the NFL season on Lineups.com and ELDORADO.