The always entertaining Urban Dictionary defines a "fair weather fan" as follows: "A fan of a sports team who only shows support when the team is doing well. During hard times they usually bandwagon other teams. They basically have no real loyalty to the team, but still manage to get better seats than you at the game."
And another definition: "Certain people who only watch a sports team when said sports team is having a winning season."
So, to sum up, a "fair weather fan" only cheers for his team when it's winning. In the NFL, it's someone who only throws on a jersey and face paint when his squad is constantly competing in the playoffs or for Super Bowl rings.
If not, they'll jump on the bandwagon of the "it" team—like the Green Bay Packers this year—and give all their support to that squad because they're currently winning.
But which NFL fanbases are the most likely to do this? Well, let's take a look at the top 10.