NFL officials put a special mark or stamp on each ball approved for use on offensive possessions, as well as the “K balls” used on special teams, to ensure only properly inspected and approved footballs are used in that game. Walt Anderson, the referee for the AFC title game, had personally inspected and marked each of the footballs that were approved for use in that game.

The alternate official, Greg Yette, became suspicious when he noticed that the football McNally handed him did not have the proper markings on it, three sources said. One of those sources added that Yette found it surprising that the officials’ locker room attendant was on the field, trying to hand him a ball, because officials’ locker room attendants don’t typically have ball-handling responsibilities during NFL games. Once McNally tried to introduce the unapproved football into the game, the source said, Yette notified the NFL’s vice president of game operations, Mike Kensil, who was at the game in the press box.

Sources said they are not sure at what point during the first half McNally tried to introduce the impermissible football to Yette. They didn’t know his motivation for doing so, either. Yette, when reached by Outside the Lines, declined to comment.