Where you hit the cue ball decides what it does after contact. Hit it dead center and it travels straight. Hit it off-center and you add spin, which is how good players control where the cue ball ends up for the next shot. This post walks through the main kinds of spin: side english, draw, follow, and the swerve that side spin can cause.

What is spin in pool?

Spin is rotation the cue ball carries as it moves. A center-ball hit sends the cue ball into a short slide and then into a straight roll, with no extra spin working for or against you. The moment you strike off-center, you put spin on the ball, and that spin changes its path off a cushion and its behavior after it hits the object ball.

What is english (side spin)?

English is side spin, which you get by hitting left or right of center. It does two things. It changes the angle the cue ball takes off a cushion, so you can widen or tighten the bounce. It also adds throw on the object ball, nudging it slightly off the line you would expect from a clean center hit. Side spin can also bend the cue ball's own path slightly, a swerve that grows more pronounced when the cue is raised.

What is the difference between draw and follow?

They are opposites, set by hitting above or below center. Hit above center and you get follow, which is top spin: the cue ball keeps rolling forward after it contacts the object ball. Hit below center and you get draw, which is back spin: the cue ball comes backward after contact. Both let you place the cue ball for the next shot instead of leaving it wherever it happens to stop.

How much spin can you put on the ball?

Not as much as you might want. There is a physical ceiling called the miscue limit. RealPool soft-caps the tip offset at about 0.48 of the ball's radius, because past that point a real cue tip slides off the ball instead of gripping it and the shot miscues. The engine clamps the offset there, so you can lean on spin but you cannot push it past what a real player could actually hit. Take the spin all the way and tilt the cue steeply and you are into massé territory, where the cue ball curves on a tight arc.

How RealPool turns your aim into spin

RealPool does not fake any of this. When you take a shot, the function that turns the strike into motion, cueStrike, reads your tip position (how far off-center you hit) plus the cue elevation and maps that into the cue ball's spin. Hit high for follow, low for draw, to the side for english: the spin vector follows the contact point. The numbers are seeded from David Alciatore's published technical proofs on billiard physics (TP A.30).

After the strike, cloth friction takes over. The ball goes through a faster sliding phase with higher friction, which bleeds into a slower rolling phase, and the spin grips the cloth and bends or checks the path along the way. Some energy is lost at the tip on every hit: cue-tip efficiency is about 0.87, so roughly 13% of the energy goes away per strike, and the cue and ball carry a mass ratio of 6oz ball to 19oz cue.

If a term in this post is new to you, the glossary has short definitions, and the 8-ball rules cover what is legal once you start using spin in a real game. Spin is physically grounded here, not scripted, so the only way to get a feel for it is to hit some shots.

Common questions

What is spin in pool?

Spin is rotation on the cue ball. A center-ball hit makes the ball slide and then roll straight, with no extra spin. Hitting off-center puts spin on the ball, which changes how it comes off a cushion and how it behaves after it strikes the object ball.

What is the difference between draw and follow?

Follow comes from hitting above center. The cue ball keeps rolling forward after it contacts the object ball. Draw comes from hitting below center. The cue ball comes backward after contact.

How much spin can you put on the cue ball?

There is a physical ceiling called the miscue limit. Past a tip offset of about 0.48 of the ball's radius, a real cue tip slides off the ball instead of gripping it. RealPool clamps the tip offset at that point, so you can lean on spin but not beyond what a real player could hit.