The Poison Ball

Option 6. Poison
A version of the game allowing “poison” balls is popular. A poison ball is one that has scored all the wickets but hasn't hit the finishing stake. A poison ball may hit any opponent ball and have it removed from the game. Conversely, if an opponent ball hits a poison ball, the poison ball is removed from the game. If a poison ball fully passes through any wicket in any direction, it is removed from the game.

A poison ball does not earn bonus shots for hitting other balls.
(croquetamerica.com)

Well, I guess that settles that. When I was growing up in Lincoln we allowed one extra shot after the poison ball hit an opponent ball. My family up here, for the most part, goes by the official rules. However, I have never played by the rule that an opponent ball can strike the poison ball, thus eliminating the poison ball. Weird. In any case, croquet is a fantastically fun game (though you might not think so at first glance) and is best played with a hearty dose of extended family members. If there does happen to be a dispute, it might be best to settle it by asking the person whose house you are playing at, or whose set you are using.