The advantage of wind must have felt fairly strong to Belichick. His team captains thought he was crazy. At the time, it was impossible to tell from the comfort of my sofa how bad the wind was, but I was curious if we could see the effect statistically.
Scott Kacsmar at Football Outsiders did a good review of the game (and has an excellent breakdown of how games have been decided in the nearly two seasons of the new format). It's clear how the wind would affect the kicking game, but Belichick's biggest risk was that there would be no kicks at all--a Denver TD would mean his team would never touch the ball. So I looked at passing stats.
I thought the best way to look at things would be raw yards per attempt (YPA). I didn't use net yards (which includes sack yards) or EPA/WPA which factor in almost everything including fumbles and penalties, because those things aren't driven by the wind. And if the wind was such a big factor, we'd see it in the raw average without worrying about adjustments.
NE defended the north end zone (had the wind at its back) in the 1st, 4th, and OT periods. DEN had the wind in the 2nd and 3rd periods. The table below lists the YPA for the team going into the wind and the team with the wind for each period. DEN's numbers are in orange, and NE's are in blue.
|Period||Into Wind||With Wind|
It turns out that offenses going into the wind actually had a higher average YPA. But Manning did throw his single pick of the game when going into the wind. NE's 3rd quarter featured a 33-yard pass and a 43-yard pass, which are the primary drivers of the results. Setting those two plays aside, if only to see what affect they had on the averages, the results are 4.5 YPA for into the wind and 5.1 YPA against the wind.
So even if we throw out the two biggest pass plays of the game, which happened to be into the wind, there still isn't a clear statistical difference in YPA between having the wind at the offense's back and having it in their faces.
I assume Belichick was talking to Tom Brady about the passing conditions all game. Brady is experienced, so his opinion would be the one that counts. And it would only take about an effect of about 6% of Win Probability for the wind to swing the advantage. The one thing we know for sure is that Belichick's decision wasn't correct because his team won. That's pure hindsight bias.