There's no reason you can't have EBs on in a league IMO. It will be a problem if you let players have EBs on games where the ball times are longer but on an old add-a-ball em, or even most solid state games, EBs are not likely to hold up tournament progress with the far shorter ball times. The only possible issue I can imagine is that the rules will vary from title to title so you'd need to have it clearly marked for players to see.

EBs - as in shoot agains? I believe in plunging those out. Hitting flipper buttons BEFORE launching ball is ok, after that you can't touch it. Games can just go way too long if you are playing EBs - really? We need EBs on LOTR and SM? And it's just not done. A tournament with EBs is kind of amateur hour.

But AAB games (specifically 70s WOW gottliebs) I believe you play as is. Most AAB games are pointless if you aren't going for WOWs, it's the point of the game. And it would be harder to keep track of how many balls you have played anyway. So in my IFPA tournaments we make exceptions if there is an AAB wedgehead on hand.

IF people don't go for that, recuse AAB games from play.

We have a Diamond Jack in league, and we definitely allow AAB. EBs are otherwise Off in the software for all other games.

So if extra balls are not allowed on solid state games
then how do you play games like Centaur.
Or I guess you might consider that a multiball mode.

On an AAB pin like Melody, you are not going to worry that games last too long
as with that game it is so hard to earn an added ball anyways.
Pop a Card though is a AAB pin where it might be too easy to earn added balls.

Some AABs can be set for novelty play, earn extra points instead of extra balls.

For PAPA and Pinburgh, there are no exceptions. All games play "as is" -- if it's giving extra balls, you play them. When possible, extra balls are shut off in software, but it's not always possible. Bonus balls and timed balls are also played, such as Medusa's earned bonus time ball.

Any other rules about extra balls are house or league rules, including the rules to plunge EBs or flip once or play only 1 EB per player.

I'm not sure that an add-a-ball game is a great idea for tournament play because a good player might play forever. In that case I would go with the one flip rule as mentioned. A lot of EMs have no extra balls. For those that do, I usually prefer to play them out. A great example is Target Alpha. With this game the drop targets don't reset during the ball, so there is sort of a limit on the scoring for each ball to 15,000 plus whatever you get banging the ball around. Getting an extra ball or two is what sets a great game apart from a good game.

The problem with setting a "one-flip rule" or something like it for tournament play is that it requires vigilance to enforce. Normally, you can just let someone play, then record their score when the game's over -- if there is a plunge-EB requirement then a scorekeeper has to watch that game carefully at all times; then if a player plays an EB without knowing, what's the enforcement? These are all reasons to avoid games where EBs can't be shut off, but to let it go if necessary.

I agree with you that certain add-a-ball games should be off limits because they could, unfortunately, take a very long time.

For larger tournaments this type of vigilance can't be 100% confirmed for everyone. There have definitely been issues around this at events, both in qualifying and finals, where players didn't know whether to plunge or play. It's another reason to make it always "play as is" if it's a large public event. For small private events and leagues, no problem to make or enforce this rule

There aren't any add-a-ball games in the PAPA collection that I know of, which is probably why there aren't any game notes about them. I'm not familiar enough with add-a-ball games to know what to include or exclude, sorry!