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Originally posted at harvardsportsanalysis.org

After the Philadelphia Eagles close loss to the Arizona Cardinals a few weeks back, Eagles players and coaches blamed much of their failure on turning the ball over in the red zone. “You turn the ball over twice inside the red zone,” Head Coach Chip Kelly stated, “you’re gonna lose the football game.” Other coaches denounce red zone turnovers with equal or greater fervor, such as when Jay Gruden went so far as to call them “inexcusable” after the Redskins-Texans matchup in September.

While conventional football wisdom states that red zone turnovers are especially costly, analytics research has often said the near opposite. In The Hidden Game of Football, a seminal work introducing the world to football analytics, Pete Palmer and Bob Carroll present the controversial idea that a turnover has a constant value of negative 4 expected points regardless of field position.

 

Hidden Game of Football: Expected Points by Field Position
Hidden Game of Football: Expected Points by Field Position

The linear nature of this graph implies that a turnover at any field position is just as costly as the same turnover that occurs somewhere else, even 90 yards away. The idea behind this theory is that when a turnover occurs, there are two simultaneous effects that need to be considered. First, the team that gives up the football loses the expected points from its current drive. Second, the recovering team now gains expected points based on field position. So a turnover in the red zone, while costing the offense between four and six points, also leaves the opposing offense with over 80 yards to gain and an expected point output of between minus two and zero.

This theory was created in the late 80s, well before we had the more accurate and empirical expected points frameworks that now exist. In 2003, Aaron Schatz of Football Outsiders revised these estimates with an Expected Points analysis. Thanks to Advanced Football Analytics and their expected points model, we can update that analysis estimating the point value of turnovers in the NFL based on field position and down. The red zone refers to the field position within 20 yards from the end zone and the “deep zone” as I will call it, refers to positions within 20 yards from a team’s own end zone. In the chart below, one can see the cost of each type of turnover demarcated by down using a seven period moving average.

Change in Expected Points of NFL Turnovers by Field Position
Change in Expected Points of NFL Turnovers by Field Position

The first thing to notice about the graph is that turnovers on earlier downs are much more costly than those on later downs. This is because 1st down and 10 from a certain field position has a much higher expected point value than 3rd and 10 from the same spot. This makes sense as a turnover on 3rd down is just delaying the mostly inevitable change in possession that would occur from a punt on fourth down anyway (although the better field position from the turnover results in this being a negative expected point play).

Another interesting thing to note is that turnovers are clearly more costly close to either goal line than in the middle of the field. In fact, for each down situation, the least costly field position for a turnover is the 50-yard line. At the tails of the graph, we see that a red zone turnover isn’t necessarily worse than a turnover in the deep zone except for on 2nd or 3rd down where red zone turnovers are slightly more costly than deep zone turnovers

So is the value of a turnover really constant like early analytics would suggest? Definitely not. However, football traditionalists are also wrong by overemphasizing the importance of red zone turnovers when there are other places on the field where it is just as damaging to give up the ball. The next time you hear someone condemning a red zone turnover, consider the idea that 1st down turnovers and deep zone turnovers deserve at least some of the attention currently given to red zone turnovers.