The 2020 version of the FIPJP rules contains new rules about throwing the jack. Naturally, this means that players have new questions. Here is one that was recently posted on Ask the Umpire.
This question was prompted by the 2020 rules revision, but Article 6 has always said that the jack must be thrown on the assigned terrain. So the real question is— What does it mean to say “on the assigned terrain“? A hit jack straddling a dead-ball line is considered to be live. Is a thrown jack straddling a side guide line considered to be “on the assigned terrain”?
Mike Pegg’s answer was NO… “The jack can be thrown up to the side line, but not on or over it.” Mike’s opinion is that in order to be “on the assigned terrain” the thrown jack must be COMPLETELY inside the guide lines of the lane; it must not be straddling or even touching a guide line.
The editors of boulistenaute.com disagree. This diagram from boulistenaute.com clearly shows a valid thrown jack straddling a side line.
History and earlier versions of the FIPJP rules don’t really offer any insight, because this issue simply never came up. In the past, if the adjoining lanes were dead ground, the jack always had to be at least 50cm away from the sidelines. If the adjoining lanes were live ground, there was no reason to care very much about whether or not the thrown jack was straddling a guideline. I think that if you travelled back in time to, say, 2016 and asked around, most umpires would probably say YES: a thrown jack straddling a guide line between two live terrains is valid.
The bottom line is that the written rules do not define “on the assigned terrain“. The rules do clearly say that a boule or a hit jack is still alive if it is straddling a dead-ball line. Reasoning by analogy naturally leads to the conclusion that a thrown jack is valid if it is straddling a guide line.
If you’re playing in a competition and this situation comes up, what kind of decision can you expect from the umpire? Well… who knows?
[This post was revised 2021-01-02 after further thought and research led me to change my opinions on this topic. I've deleted or edited comments on the first version of this post that refer to opinions that no longer appear in this post.]