NFL Playoffs: The "Hot Team" Myth of NFL Regular Season Momentum

The NFL is down to the Final 12.  Eight division winners and four wild card teams begin the tournament that decides the NFL champion. 

Fans and observers often predict the tournament results and, because no one can quit while they’re ahead, to provide an erudite justification for their picks.   As the legions struggle to predict the unforeseeable, we will also witness the perennial stampede of archaic and foolish sports clichés. 

Here's some of the more palling pabulum:

• It’s going to come down to which team wants it more.  Because, you know, there are some fellas down there who are really just texting it in at this point in the season.
• Intangibles are key come playoff time.   More important to my explanation, intangibles are unquantifiable so you can’t argue with those numbers.
• This team likes to take a punch before they get mad enough to fight back.  Yeah, give your opponent a few chances to knock you out before you start playing.  A sure fire winning recipe.
• The game isn’t played on paper.  Although, paper may be a better playing surface than the Lambau Field permafrost.
• They have the confidence to go all the way.   Of course every NFL player has more confidence in his little toenail than the rest of us can cram into our SUVs.
• The team that gets hot will win the championship.  How do we know who the hot team is?  It’s the team that wins the Super Bowl.  Why do they win the Super Bowl?  Because they’re the hot team!  They won the last three of four games, at least.  Duh.
• This team will go far because they have a lot of momentum coming into the playoffs.  Hmmm, perhaps this one is actually verifiable.

“Momentum” is an interesting concept in sports.  Everyone who has played competitive sports knows the experience of playing with momentum, as well as being on the receiving end of a team who has it. 

When you have momentum, the game slows down, the ball gets bigger, your opponent can’t walk and chew gum, every decision is the right call, you don’t tire and inspiration and creativity release your body to perform physical feats you’ve never done before.

Conversely, when your opponent has momentum, your brain slows down, you can’t see the ball, your opponent can’t do anything wrong but you do, you can’t catch your breath and the simplest tasks that you’ve done thousands of times suddenly become impossible.

This kind of momentum is, however, fleeting, fading into the mists as quickly as it appears.  The method for creating and replicating momentum is the holy grail of coaching. 

So momentum is ephemeral and darn near impossible to induce.  But can it be measured?  More importantly to the sports mob, does it predict success going forward?

In the context of NFL playoff prediction, momentum refers to a team’s performance going into the postseason.  The argument holds that a team who is “winning” will, for a variety of reasons, continue to win. 

It should be possible, then, to simply look at a team’s winning streak at the end of a season and compare it to their performance in the playoffs. 

The NFL expanded the regular season to 16 games and the playoffs to 12 teams in 1990.  I compiled a dataset of all 264 playoff teams since 1990 and looked up each team’s end-of-season win streak, or “ESWS”.  If the cliché is true, then a team’s ESWS should predict their playoff success.

Some playoff teams lose their final regular season game.  The table below breaks down playoff success and the proportion of teams at each level of success that won their final regular season game (ESW%).

	Super Bowl  Champ	Super Bowl Finalist	Conference Finalist	Divisional Round	Wild Card Round
Avg. Wins	12.2	12.4	11.7	10.8	10.0
Win %	76%	77%	73%	69%	63%
ESW %	82%	64%	77%	64%	69%

The 22 Super Bowl Champions since 1990 won 76 percent of their regular season games, but 82 percent of the Super Bowl teams won their final regular season game.  It is a small difference, but it does suggest that end-of-season wins (ESW) are more important than other regular season wins to Super Bowl champions.

Super Bowl championship teams also won more of their final regular season games than the teams they beat, the Super Bowl finalists (82%-64%).  This is some clear evidence that winning the last game of the season matters.

However, as we move across the table the data becomes less clear, more like a dirty window screen really.  The conference finalists won a larger percentage of their regular season games than the Super Bowl finalists (64 percent, as opposed to 77 percent) an indication that winning the last game doesn't matter.  

When we move across to the next column, we see the teams that lost in the divisional round did not win as many end-of-season games as the conference finalists (77 percent, to the losers' collective 64 percent), but they did win as much as Super Bowl finalists, both at 64 percent.  The losers in the Wild Card Round, of course, had slightly better end-of-season success than teams at the next level, five percent higher than the 64 percent. 

If winning the last game of the regular season mattered to postseason success, we would see the ESW percentage decline as we move across levels of playoff success.  Instead, the Super Bowl champs have the highest ESW percentage, but it doesn't seem to matter to any other level.

Now maybe the last game of the regular season is not a good measure of momentum.  Odd things happen in Week 17, as many teams have "given up" or "have nothing to play for," which is why most fantasy football leagues hold their championships the week before, the penultimate week of the season.  The table below gives the percentage of teams at each level of playoff success that had an ESWS of two or more games  (ESWS > 1).

	Super Bowl    Champ	Super Bowl    Finalist	Conference   Finalists	Divisional   Round	Wild Card   Round
ESW %	82%	64%	77%	64%	69%
ESWS>1 %	55%	63%	48%	38%	45%

Just like the first table, their is no obvious pattern in the data.  In fact, the Super Bowl champions have fewer end of season winning streaks of two or more games than the teams they beat in the Super Bowl.  The teams that lose the Wild Card game have more ESWS of two or more games than teams in the Divisional Round.  Again, there there doesn't appear to be any causal relationship between momentum and playoff success.

Ok, one last table, I promise, and if you've read along this far go open a beer to reward your perseverance.  Ready?

In the last table I compute the average length of the ESWS at each level of playoff success.  I then divide this by the average number of wins.  The result is the proportion of total wins that came in the end of season win streak, or percentage ESS.  The more wins you have rolling into the playoffs the better, remember?

	Super Bowl    Champ	Super Bowl    Finalist	Conference    Finalist	Divisional   Round	Wild Card   Round
Avg. Wins	12.2	12.4	11.7	10.8	10.0
Avg. ESWS	2.6	3.1	2.6	1.8	1.6
% ESS	21%	25%	22%	17%	16%

Yet again, the highest playoff performers (the Super Bowl Champions, of course) have less momentum at the end of the season than their opponent and the conference finalists.  The losers in the divisional and wild card rounds have smaller winning streaks at the end of the season, but only by a few percentage points.  

There is simply no relationship between a team's momentum at the end of the season, as measured by the end of season win streak, and their level of performance in the NFL playoffs.

I have no doubt that someone will respond in the comments below that stats don't tell the whole story. I know this because that is what sports fans tend to do.

Enjoy the playoffs.

[Next week:  Is there a Bye Week advantage?