According to rule 1-21 #2. of the BCAPL rules, if you foul, your inning ends. So, if he knew he fouled, and kept shooting anyways, you could apply a shooting out of turn foul, or an unsportsmanship foul on him. [...].
Yes, the situation Prad mentioned involved a shooter who fouled, admits the foul, and chose to shoot again. That's not OK and is not in fact different from scratching and then pulling the cueball out of the pocket and shooting again.
I was the TD for Prad's situation (his teamate's situation actually).
Here is the deal at Fargo Billiards
In unrefereed matches, the opponent
IS NOT the referee.
Let's look at some of the consequences of thinking otherwise. If the opponent
IS the referee, then the opponent should never be sitting in a chair; he should be moving around the table to get in the best position to see each shot. He should stop the shooter from shooting on occasion to look at the shot from the shooter's perspective before getting into position. He should stop the shooter from shooting if a server or patron walks between him and the shooter. And he should stop the shooter from shooting while a server asks him whether he needs ketchup with his fries. Clearly it would be obnoxious for an opponent truly to act like a referee.
So what then is the role of the opponent? The opponent, unlike a non-playing teammate or railbird, has a general obligation to pay attention, has the right to question whether a hit was legal, and has a right before the shot to request an agreed-upon third party be an ad hoc referee.
The main obligation is on the shooter. The shooter is the referee. He has an obligation to call a foul when a foul occurs. If the opponent questions a shot after the fact, the shooter has the obligation to listen, consider, make an honest assessment, and ultimately make the call. The shooter also has a general obligation on a shot that might be close to alert his opponent, who might want to request an ad hoc referee.