Throw is the small error between where you aim the object ball and where it actually goes. When the cue ball and the object ball touch, the friction between them pushes the object ball a little to one side of the straight, pure-geometry line. Aim by simple geometry alone and the ball often misses by exactly that nudge.

What is throw in pool?

Throw is when the two balls make contact and friction between their surfaces drags the object ball slightly off the line you aimed. Pure geometry says the object ball leaves along the line through the two ball centers at contact. Throw is the real-world deviation from that line, and on longer shots it is enough to rattle a pocket or miss outright. If you want the vocabulary around it, the pool terms glossary lays out the related words.

What causes throw?

There are two kinds, and they can stack on the same shot. The first is cut-induced throw. On an angled cut the cue ball is not driving straight into the object ball, so as the surfaces slide past each other the cue ball drags the object ball a little sideways before they separate.

The second is spin-induced throw. If the cue ball carries sidespin (also called english) into the contact, that spin rubs off onto the object ball and pushes it off line in the direction of the rub. This is the same spin you read about in spin in pool, just seen from the moment of ball-to-ball contact rather than the cue ball's own path.

Why do slow and thin shots throw more?

Throw gets bigger as the shot gets slower and the cut gets thinner. The reason is grip. When the two ball surfaces slide past each other slowly, the contact grips harder and transfers more sideways force. A fast, full hit slips through quickly and throws less.

A thin cut keeps the surfaces sliding for longer relative to the forward push, so the gripping contact has more chance to drag the object ball aside. Combine a thin cut with a soft roll and you get the most throw of all, which is why a gentle long cut is one of the easier shots to miss.

How RealPool models throw

RealPool does not paint throw on after the fact. It comes out of the friction between the two balls at contact, the same way it does on a real table. The engine uses Marlow's dynamic-friction fit, taken from David Alciatore's technical proof TP A.14: the friction coefficient is high when the two surfaces slip past each other slowly, and it falls as the slip speed rises.

That single curve gives you both behaviors for free. A slow or thin contact slips gently, so the coefficient stays high and the ball is thrown more. A fast, full contact slips quickly, the coefficient drops, and throw is small. The sideways (tangential) impulse is capped by the 1/7 no-slip limit, so the contact can grip but never over-rotate the object ball past what the physics allows.

Because the deviation falls out of the contact math instead of a lookup table, it is consistent with everything else the simulation does. If you are curious how that determinism is built, see the deterministic physics engine. The practice sandbox is the place to feel throw for yourself: line up a slow thin cut and watch the object ball drift off the geometry line.

Common questions

What is throw in pool?

Throw is when the cue ball and object ball touch and friction between them pushes the object ball slightly off the straight, pure-geometry line you aimed. The ball ends up a little to one side of where simple aiming says it should go.

What causes throw on a pool shot?

Two things. Cut-induced throw happens on an angled cut, where the cue ball drags the object ball sideways as the surfaces slide past each other. Spin-induced throw happens when sidespin on the cue ball rubs off onto the object ball at contact.

Why do slow and thin shots throw more?

The two ball surfaces grip harder when they slide past each other slowly. A slow shot or a thin cut both keep the contact gripping rather than slipping, so more sideways force transfers and the object ball is thrown further off line. Knowing this matters when you play the 8-ball pool rules for position, since a thrown ball can turn a make into a miss.