Research examines momentum in the NFL

The word, "momentum," is often described by coaches, players, sports writers and announcers as those defining points in the game that causes a team to win or lose. "However, it is often difficult for human perception to separate intrinsic changes in probability from simple, random occurrences," Fry says.

In their paper, "Searching for Momentum in the NFL," the researchers analyzed data on five years' worth of plays during the NFL season, from 2002 to 2007. They examined four particular plays that are popularly described as "momentum-changing events:"

1. Successful fourth-down conversions

2. Unsuccessful fourth-down conversions

3. Turnovers

4. Allowing scores (touchdowns and/or field goals)

For each of the events, the researchers compared a team's performance up to the "momentum-changing event" to plays from a control data set. The data set used pairwise matching to control for field position, score differential, time of game and for whether the team was playing at home or on the road.

The researchers say their analysis found possible statistical evidence of positive momentum gains after a team successfully converted a fourth-down. They found no statistical evidence of in-game momentum resulting from turnovers or allowing scores.

Momentum is taken very seriously in the NFL and can be a turning point for coaches as they plan team plays.

"While our findings cannot conclusively disprove the existence of momentum in the NFL, they further support the argument that momentum should not be a guiding factor for in-game decision making," write the authors.

"We conclude that in many instances, players, coaches and writers may put too much credence on the existence of momentum and that this may affect play-calling," conclude the authors.