...It's such a grotesque image as to be hilarious:

"The billiard sharp whom anyone catches,
His doom's extremely hard:
He's made to dwell in a dungeon cell
In a spot that's always barred.
And there he plays extravagant matches
In fitless finger-stalls,
On a cloth untrue
With a twisted cue
And elliptical billiard balls !"

Now, all you billiard sharps, what does "barred" mean in this context? I know it on the guitar, but this is a ball of another color.