The set can be used by various people in various ways. Here are some use cases for the files:
Custom avatar generator
Online games (player graphics)
American football forums as default icons
Help & Credits
Documentation in HTML format included. It will show you around the file structure, group and layer names, showing you some quick tips on how to edit and extend the original icons.
Original design used with the kind permission of Luke Sedgeman (sedgeman.com).
Luke originally designed only 3 players (Brett Favre, Joe Montana and Tim Brown). I just went completely mad with this and made uniform models for all the professional teams I could ever think of. With some help from Wikipedia.