Quoted from TimMe:Check the 6th position switch on the ball count unit. Even though the GAME OVER light is coming on, if the 6th position switch isn't being pushed open by the post on the ball count stepper gear, then the ball return (O) relay and the playfield will continue to get power. As long as it has power, the O relay will pull in when the ball is sitting in the shooter pocket. When the O relay is pulled in, the replay button is disabled - and you can continue to launch the ball with the flipper button.
The position switches on the ball count unit are on the back side of the unit (opposite side from the disc and wipers).
- TimMe
In addition to this, Pro Football has a custom ball count unit built specifically for that game with two (probably four? Would make sense for 3-ball play, only counted two though) extra rivets on it for the special outhole kicker to disable at the end of the game. Make sure they are clean and that the jumper between the wiper fingers is intact. This may just control the apron light, but that wouldn't make sense as the contacts wouldn't touch unless in game over.