When a player mistakenly plays somebody else’s boule, it is not considered to be a boule played contrary to the rules. Instead, Article 23 (“A player throwing a boule other than his own”) says—
The player who plays a boule other than his own receives a warning. The boule played is nevertheless valid but it must immediately be replaced…
The idea behind this rule is sensible, but the rule is defective— it doesn’t say WHAT we should use to replace the mistakenly-thrown boule.
Bob accidentally throws a boule that is not his. Bob still has at least one unplayed boule.
This is the kind of situation that the rule was designed for. The resolution is clear. The boule that Bob played is picked up and replaced by one of Bob’s unplayed boules.
Bob accidentally throws a boule that is not his. Bob has no unplayed boules of his own.
If Bob accidentally threw a boule belonging to one of his team-mates, the solution is simple solution— leave the boule where it is. If the accidentally-played boule did NOT belong to one of Bob’s team-mates, but his team still has unplayed boules, again the solution is simple solution— replace the thrown boule with one of Bob’s team-mates unplayed boules.
Note however that in this case, Bob not only threw a boule that wasn’t his, he threw more boules than he was allowed to throw. A strict umpire might rule that the thrown boule was played contrary to the rules, and that the opposing team may apply the advantage rule in Article 24. A very strict umpire might also disqualify one of Bob’s boules in the next mene.
Bob accidentally throws one of the opposing team’s unplayed boules. Bob’s team has no unplayed boules.
Here is where we run into problems, because there is no boule that Bob’s team can use to replace the mistakenly-thrown boule. The umpire will probably rule that the thrown boule was played contrary to the rules, and that the opposing team may apply the advantage rule in Article 24. They can either leave everything where it is, or undo the throw (as much as possible).
Because Bob threw more boules than he was allowed to throw, the umpire may also disqualify one of Bob’s boules in the next mene.
Bob accidentally throws a boule that is not a live boule in the game. Bob’s team has no unplayed boules.
This can happen when a player forgets that he’s in a triples game (not a doubles game).
He forgets that he’s allowed to throw only two boules (not three), and he throws a third boule. Rarely, it can happen when a player picks up and throws a boule that has already been thrown. In either case, the player accidentally introduces a foreign object into the game, as if a cow had wandered onto the terrain.
If the thrown boule changed nothing on the ground, the boule is simply removed. On the other hand, if the thrown boule DID change something on the ground, Article 22, Displaced boules applies.
If a stationary boule is moved by the wind or slope of the ground, for example, it is put back in its place, provided it has been marked. The same applies to any boule accidentally displaced by a player, an umpire, a spectator, an animal or any moving object.
Article 12 says the same thing about the jack. So we remove the boule and put everything that was marked back where it was. (See Mike Pegg’s answer to this question on “Ask the Umpire”.)
Again, because Bob has thrown more boules than he is allowed to throw, the umpire may also disqualify one of Bob’s boules in the next mene.