I happened upon this fact purely by mistake. I just happened to see a tidbit on Terry Bradshaw, and he said he was the back up to Phil Robertson. The story goes that Phil liked hunting ducks and eventually quit football and that's when Terry took over.

So I did some more searching and found Phil talking about Terry, confirming the story. Then I found old footage of Phil Robertson playing football. Here it is for you to check out.

Here's Phil talking about Terry

This is Phil Robertson playing Ken Stabler (who went on to play for the Oakland Raiders)