EdjSports (some analytics house) via Football Outsiders:
The set of game variables (clock, field position, score) in this decision came together in a perfect storm, greatly magnifying the impact of this fourth down decision. Make no doubt about it, this was an aggressive call. Perhaps surprisingly, the simulation model from which we derive our usual aggressive fourth down stance actually disagreed with Coach Reich. The Edj model was in favor of punting the ball and estimated that the GWC (game winning chance) sacrificed by going for it was 3.5 percent. This conclusion was further supported by substituting a top passing offense and weak passing defense into the simulation. Even under that extreme scenario, the punt is still the top choice.
An important assumption that enters the model’s assessment is the value of a tie. The model values a tie as half a win. It’s important to note that Coach Reich is likely valuing a tie much differently than the model. He made this clear in his postgame press conference by declaring, “I’m not playing to tie.” To try to account for this difference in assumptions, we re-assessed this decision by assuming it occurred in the postseason when tie games are not an option. In this alternative scenario, the Colts would need to convert the fourth-and-4 approximately 81 percent of the time to justify the more aggressive approach. Historically, NFL teams would be expected to succeed closer to 50 percent. Again, we see the punt being favored.
To unpack this surprising finding a bit, the Colts’ field position played a significant role in this decision. At their own 43-yard line, the Colts were at an important threshold of the field. From their own side of midfield, they could expect to receive the maximum benefit from swinging field position with a punt. To hone in on this effect, we ran a sensitivity analysis by varying the yard-line where the Colts faced this fourth-and-4 decision, keeping all other game variables constant. We found that the “crossover” point or the yardline where the two decisions reached parity with one another in terms of GWC was the Indianapolis 48.