I heartily disagree about slop. I see time and time again, either a slam on the 9 or another ball that goes in to be able to continue a run and that is just not right. It rewards new players to just crank on a shot, instead of using finesse. Especially in a weekly race to 3, it can be devastating. At higher skill levels you do not see as much slop, because usually the player knows where everything is going. I think it should still be a win on the break though, just as an 8 ball is in many rules, and that would be the only shot that would not need to be called. Any ball that goes stays down.
A friend wants to run a league and they have requested Call 9 ball. She asked me what would happen if the 8 went into the wrong pocket.
I like these rules.
In call 9 ball, in the situation you described, if it went into an uncalled pocket, it would be loss of game like 8 ball, therefore cutting down on the slamming effect and making it more of a skill game. If you called a ball and ALSO wanted to call the 9 as insurance, you would call the likeliest pocket. If the 9 did not go, but the first called ball did, you would keep shooting. (First called ball is your primary ball, 2nd called ball is secondary and you are not penalized if it does not go in.) Some people think that with those rules, that everyone would just call a 9 ball on every shot. The reality is that most players do have a pocket in mind when they ride the cheese and the ones who fluke it from nowhere aren't going to call the right pocket anyway, because they never saw the shot in the first place.
Call 9ball also gives bragging rights to someone who clearly saw a shot and executed it and observers can learn from it and start seeing possibilities themselves. It also removes the stigma of slop when it was a great shot.
If it is a different ball than the 9 that gets fluked in, it spots.