The NFL is a Week-to-Week League: Should I Bet Teams Following a Win?

I am a firm believer that momentum does not carry over in the NFL. Thursday games can be different, but 6 days off between matchups normally creates a clean slate.

If momentum did exist in the NFL, we would expect to see things like an increased chance of winning after a win and an increased chance of losing after a loss. I am going to dig up some numbers that will finally help put this myth to rest and answer the question: does momentum exist in the NFL?

Results Following a Win

I love looking at trends based on previous outcome. It fascinates me. I wanted to begin by looking at how NFL teams typically perform following a win the previous week. I will explore both the ATS and SU win percentages to see if “hot teams” can give us some sort of advantage.

Year	ATS %	SU %	Avg Line
2018	52.5%	55.9%	-1.2
2017	47.8%	54.2%	-1.7
2016	51.3%	55.7%	-1.1
2015	53.0%	55.4%	-1.0
2014	47.9%	52.9%	-1.4
2013	47.6%	53.6%	-1.3
2012	48.9%	55.0%	-1.5
2011	50.6%	57.5%	-1.8
2010	47.9%	49.2%	-0.7
2009	51.9%	57.1%	-1.8
Total	49.9%	54.6%	-1.3

Here are my takeaways from this table. First, there is absolutely no trend in ATS win percentage. It is right around 50% each year. If momentum does exist in ATS numbers, the books must compensate for it perfectly because there is no advantage to be gained by betting a team to cover who has just won.

Second, just because the SU win percentage following a win is greater than 50% does not mean momentum exists. With an average line of -1.3, these teams need to win about 54.5% of their games to break even. The 10-year SU win rate of 54.6% with a -1.3 line is trivially profitable.

Think about it from a logical angle as well. Good teams who have winning records are going to be following up a win much more often than poor teams with losing records. Thus, our sample of teams following a win is comprised of mostly winning teams, who you would already expect to have a decent win percentage.

Let’s break it down. This sample included 2,424 games, or about 242 per year (games in which both teams won previously are counted twice because each team is following up a win). Of those games, the team was a winning team in 1,703 of them, or 70.3%. That means a losing team (or a .500 team) was following up a win only 721 times, or 29.7%.

Results Following a Win – Sorted by Record

To better search for the existence of momentum, we need to break down post-win performances by record. I decided to divide teams into three categories: bad teams (less than 40% win percentage), decent teams (40-60% win percentage), or great teams (greater than 60% win percentage).

One last note – I think this search should not begin until Week 5 of each season. Here is why: just because a team is 1-0 does not mean they are “great”. At 3-1, however, I would give them that distinction. Waiting until Week 5 will better divide the three levels of teams and give more accurate results.

Bad Teams Following a Win

Year	ATS %	SU %	Avg Line
2018	60.0%	52.9%	2.5
2017	66.7%	58.8%	2.8
2016	68.8%	47.1%	2.4
2015	48.5%	36.4%	3.1
2014	40.9%	31.8%	4.9
2013	44.4%	37.0%	3.2
2012	38.1%	38.1%	1.9
2011	48.3%	40.0%	2.4
2010	48.6%	34.3%	2.9
2009	59.3%	42.9%	5.5
Total	50.8%	40.5%	3.2

Here is how those bad teams with a win percentage less than 40% have fared after they managed to win a game. That 50.8% ATS win percentage for bad teams following a win is actually slightly better than the 49.9% mark for all teams following a win, but it still is not a profitable win rate.

The 54.6% SU win rate for all teams following a win is right at the break-even point, considering the -1.3 average line. Well, the same thing occurs when we look only at the bad teams. With an average line of +3.2, we can expect the moneyline odds to be right around +140.

With that line, teams would need to win at a rate somewhere between 41% and 42% to break even. As you can see, the “bad teams following a win” SU win percentage is 40.5%, slightly lower than what they need to profit.

Decent Teams Following a Win

Year	ATS %	SU %	Avg Line
2018	63.8%	57.6%	-0.5
2017	47.4%	48.8%	0
2016	48.7%	53.2%	-1
2015	57.1%	47.6%	0.7
2014	50.8%	48.3%	-1.2
2013	46.8%	51.3%	0
2012	57.5%	56.6%	-0.4
2011	54.4%	60.7%	-0.6
2010	45.5%	42.1%	0.4
2009	43.9%	50.0%	-1.3
Total	51.5%	51.6%	-0.4

There is a small increase in ATS win percentage once again, but 51.5% on spreads is still not high enough to be profitable. With an average line of -0.4, teams would have to win SU about 53-55% of the time to be profitable on the moneyline.

We have seen similar stories throughout. So far, none of the win percentages we have seen are profitable. Maybe only the great teams are capable of building momentum. Let’s find out.

Great Teams Following a Win

Year	ATS %	SU %	Avg Line
2018	47.8%	60.9%	-3.6
2017	47.9%	63.5%	-4.1
2016	51.1%	60.2%	-2.2
2015	51.4%	70.5%	-4.6
2014	47.7%	61.3%	-2.8
2013	47.0%	60.0%	-4
2012	48.8%	65.1%	-4
2011	48.0%	62.4%	-4.1
2010	50.5%	59.2%	-2.7
2009	53.7%	66.0%	-4.2
Total	49.4%	62.8%	-3.6

The ATS win percentage is not profitable. 62.8% on SU bets looks pretty good, right? It seems high until you realize that the average line is -3.6. The moneyline for these bets is about -186 which means the break-even win percentage is just over 65%. These great teams could only manage 62.8% which means they would not be profitable on the moneyline.

So far, no luck finding signs of momentum.

Results for 1, 1.5, and 2-Point Favorites

Since the average line over the past 10 years for teams following wins has been -1.3, we should take a look at how ALL teams with this line have fared over that span and then compare. This presents a tricky challenge because no team is ever 1.3-point favorites. I am going to tackle this by looking at 1, 1.5, and 2-point favorites since 2009.

Here is a table illustrating how teams off a loss have fared as 1, 1.5, or 2-point favorites since 2009.

Year	ATS %	SU %	Avg Line
2018	27.3%	27.3%	-1.3
2017	38.5%	38.5%	-1.5
2016	81.8%	81.8%	-1.4
2015	42.1%	50.0%	-1.6
2014	38.5%	38.5%	-1.6
2013	58.3%	58.3%	-1.5
2012	41.2%	41.2%	-1.4
2011	40.0%	45.5%	-1.5
2010	58.8%	61.1%	-1.6
2009	44.4%	55.6%	-1.7
Total	47.0%	49.6%	-1.5

As you can see, these teams are bad bets. It might just be a bad decade for small favorites, though. So far, we do not have enough evidence to make a definitive statement as to whether momentum exists in the NFL. We need to look at teams favored by the same amounts who have just won.

Here is one more table. This is the exact same search, except this time we are looking at 1, 1.5, and 2-point favorites following a WIN, instead of a loss. Take a look.

Year	ATS %	SU %	Avg Line
2018	36.4%	40.0%	-1.3
2017	33.3%	37.5%	-1.7
2016	50.0%	57.1%	-1.5
2015	64.3%	64.3%	-1.9
2014	65.0%	70.0%	-1.5
2013	34.8%	34.8%	-1.5
2012	44.4%	47.4%	-1.6
2011	47.1%	61.1%	-1.6
2010	53.3%	53.3%	-1.7
2009	60.0%	60.0%	-1.4
Total	48.8%	52.4%	-1.6

Slightly better, but still not profitable. I have to say that we have found absolutely no evidence of momentum yet.

Verdict: Does Momentum Exist?

What did we find?

• Teams following a win are not profitable ATS or SU
• Bad teams are not profitable following a win ATS or SU
• Decent teams are not profitable following a win ATS or SU
• Great teams are not profitable following a win ATS or SU
• Teams valued by Vegas at -1.3 are not profitable, regardless of if they are following a win or loss

If momentum does exist, Vegas compensates for it perfectly because there is no edge to be gained either ATS or SU. The NFL really is a week-to-week league. In a future article, I will explore if it is worth betting or fading teams following a loss.