The classic petanque maxim is
Boule devant, boule d’argent.
The French word “argent” can mean either “silver” or “money”. I agree with Rayond Ager that in this context, it should be translated as “money”. So the maxim roughly translates as
A boule in front is a money ball.
The expression “money ball” isn’t, I think, just a metaphor for “good ball”. I suspect that it means literally that a boule in front is worth money.
In France, where petanque is of course much more popular than in the U.S., it is common to bet on petanque games and to play for money. (America a few years ago produced a movie called “The Hustler” about a pool hustler. In 2013 France produced “Les Invincibles” about a petanque hustler.) So I think that in the expression “Boule devant, boule d’argent”, “money ball” isn’t at all a metaphor. It is referring to real folding money in one’s pocket.
Finally, the old maxim has an unwritten flip-side.
If if you don’t have any boules in front — if you leave the front open and the opposing team still has boules to play — you are leaving your money on the table and asking your opponents to walk off with it.
If the front is open (le jeu est ouvert), you are inviting the opposing team simply to point right down the center and score as many points as they have boules.
So when you’re asking yourself the old question — To point? Or to shoot? — you should always ask yourself whether, if you shoot, sucessfully or not, you will be leaving the front open.