The Cut Shot

Steps

Stand behind the object ball and sight the line from pocket through its centre; mark where the ghost ball must sit.

Address the cue ball with the cue on the line to the ghost ball's centre, not to the object ball.

Stroke through with stun (a touch below centre) at medium speed; watch the object ball's line and the cue ball's.

Repeat at half-ball: the cue ball should leave at ninety degrees and the object ball with three-quarters of the pace.

On slow, thin cuts, aim a hair thinner than the geometry says — throw pushes the object ball toward the cue ball's line, so the shot plays fuller than aimed.

When it drops ten times running, take the spare ball away and see the ghost without it.

The Science

The object ball leaves along the line joining the two centres at contact, whatever you do; so aim the cue ball at the ghost-ball position, one ball's width from the object ball on the far side from the pocket. The cue ball leaves along the tangent line at right angles to that (the ninety-degree rule), carrying sin θ of the speed while the object ball takes cos θ. Friction between the balls throws the object ball a degree or two off the geometric line, more on slow shots and thin cuts — allow for it, or the long ones rattle. A rolling cue ball then curves forward off the tangent line to about 30° from where it was going; a stunned one keeps the tangent.

How It Fails

Aiming at the object ball's edge instead of the ghost ball's centre — always undercut. Forgetting throw on slow cuts — undercut again. Unintended side from a crooked stroke, which both squirts the cue ball and throws the object ball. Reading the cue ball's line as the aim line and scratching along the tangent.