Alex Karras was playing for the Detroit Lions when they played Denver in a pre-season game somewhere around 1965-66.
It was the first game played between the NFL & the AFL after the merger agreement had been reached. The leagues wouldn't fully merge for regular season play until 1970, but the Detroit-Denver game was the very first of any kind between the two leagues.
Alex Karras told the media he would walk back to Detroit if they lost to the Broncos.
They lost to the Broncos. A very miserable Karras flew back with his team, saying his statement was just a way to get the Lions fired up. He never lived that down and even Cosell made reference to it more than once.
We lost a wonderful talent in many more ways than football, and I'll miss him.