Alle sind zu A. sehr freundlich, so etwa wie man ein ausgezeichnetes Billard selbst vor guten Spielern sorgfältig zu bewahren sucht, solange bis der große Spieler kommt, das Brett genau untersucht, keinen vorzeitigen Fehler duldet, dann aber, wenn er selbst zu spielen anfängt, sich auf die rücksichtsloseste Weise auswütet.
Everyone is very kind to A., more or less as one tries to guard an excellent billiard table even from good players, until the time when the great player comes, who will carefully examine the table, will not put up with any damage done to it previously, but then, when he himself begins to play, lets himself go wildly, in the most inconsiderate manner. [Kaiser/Wilkins]
Everyone is very friendly to A., in roughly the way one might seek to protect an excellent billiard cue even from good players, until the great one comes along, takes a good look at the table, will tolerate no precocious mistakes, and then, when he starts playing, rampages in the wildest way. [Hofmann]
A cue is a Billiardstock, typically, so I think Kaiser/Wilkins makes more sense here, especially since the proprietor of a billiard table will usually have many cues and so can go ahead and play even if one is kept on reserve, but, if the table itself is reserved, then no one can play at all. The good players must have acquired their skill practicing on a different table; either that, or they are naturally good at the game.
In any case, this isn't an aphorism about billiards, but about how a certain person is treated, and specifically how the preservation of a person inviolate has less to do with consideration for that person than it does with the imperious demands of the other one, who has a claim on that person. So, sparing someone may simply be a matter of setting them up for something worse.
To me, this aphorism seems to have little in common with the others preceding it, unless you decide that the great one to come is a messiah. When the messiah comes, everything is put right, but this may involve a lot of wrecking. Is it our task to preserve things for the messiah to wreck?