At the science fiction conventions I have attended, I have many times seen groups of people in costume as a group. I've seen costumed groups depicting members of the cast of Blazing Saddles, Mortal Combat, Guitar Hero, and the movie 300 and have seen people dressed as members of a group like Stormtroopers, the Stonecutters from the Simpsons episode, Ghostbusters, Cobra Command (GI Joe), or as in the picture I posted last November, Nazis. I even saw a group of people in military riot gear conduct an intensive military style sweep of the area around the convention hotel.
As I arrived in downtown Indianapolis 5:30 Friday night, I noticed a large amount of traffic around the convention center even for rush hour. When I saw people with flags directing cars to parking lots and the clothes people were wearing, I realized what was happening. Eventually we got to our parking lot for the hotel and when we went out to dinner, the crowd was mixed with gamers and people wearing blue shirts with numbers on them.
The percentages in the chart are an estimate based on what I saw:
In clockwise order: Addai-RB, Vinatieri-K, Gonzalez-WR, Wayne-WR, Freeney-DE, Harrison-WR (no longer with team), Sanders-S, Saturday-C, Clark-TE, Manning-QB
I also saw 6 purple shirts, 3 with 28 (Peterson), 2 with 93 (P. Williams) and one with 69 (Allen).
For what it is worth, the Vikings beat the Colts in the preseason game 13-3.