How do squirt, swerve and throw differ?

Split them in time order: the launch error at the hit, the curve during travel, and the change of direction when the balls collide.

One thing to remember today

Squirt and swerve describe the cue ball’s path; throw describes the object ball’s direction changed by the collision.

Written and edited by TTBoys · How we write and check sources · Report an error

Reading the motion in diagrams

A sketch seen from above. The shot goes left to right, and the player's right is the bottom of the picture. The yellow line is the same ball over time; how much it curves, how far, and whether it crosses the aim line depend on actual conditions.

③ Throw: even on a full hit, contact friction from the cue ball's sidespin can push the object ball off the line between the centers. This is one example, thrown downward, with the angle exaggerated.

Cue ball approach
Line between centers at impact
Example object ball path with friction

A concept diagram made by TTBoys for learning. It is not a measured graph or simulation result from a paper; arrow lengths and angles are there to explain the principle.

① At the hit: squirt

With a side tip position, the cue ball can leave the cue’s aiming line toward the side opposite the tip position. With a right tip position from the player’s view, the ball first veers left; that is an example of this.

Cross’s experiments and calculations and Hyeong-Chan Kim’s cue impact study deal with the tip contact and the properties of the cue. Do not treat squirt as the same thing as a player pushing the cue out crooked.

② During travel: swerve, or curve

Sidespin with the butt of the cue raised can curve the cue ball’s path through the tilted spin axis and cloth friction. In the typical example with a right tip position, the ball first squirts left and then curves right.

The sum of the two effects changes with distance, speed, cue elevation and tip position. They do not always cancel exactly, and a ball does not keep circling just because it has sidespin.

③ Ball-to-ball collision: throw

An ideal, frictionless object ball leaves along the line joining the two ball centers at the moment of collision. Throw is the small departure from that direction caused by the relative motion and friction at the real contact surface.

The sideways motion of a cut shot and sidespin both change the relative motion at the contact surface. Do not fix the direction and size of throw from the side of the spin alone; look at thickness, speed, spin and ball condition together. Also tell an object ball that leaves in a different direction from the start apart from one that curves during travel.

An observation drill suggested by TTBoys

First, watch the cue ball’s launch and travel separately

With no object ball, film 3 center hits of the cue ball alone toward the same target.
From the same spot, keep the cue as level as you can and compare 3 hits with a small side tip position. There is no need to raise the cue to exaggerate the curve.
Mark the line just after the launch and the position at a far point separately. Watch throw with a separate two-ball layout, looking at the object ball’s starting line.

What to watch: First say whether the direction differs from the start or changes during travel, and which ball the effect belongs to.

When interpreting: If you try to measure all three effects in one shot, it is hard to separate the causes. The diagram above exaggerates the differences to explain the directions; it is not a table of correction angles.

Connect to Basics, Systems and Practice

Basics · Squirt and curve →Practice · Bridge and thickness repetition →

Evidence from papers and where it applies

Sources reviewed: 2026-10-10 · The explanations and drills are TTBoys' editing.

Experimental and theoretical paper · Rod Cross

Cue and ball deflection (or “squirt”) in billiards ↗

American Journal of Physics 76, 205–212 (2008) · DOI 10.1119/1.2825392

What this source explains: Measures and models the contact between the cue tip and the ball to explain squirt from side tip positions.

Limits: The results come from the cues, tips and test conditions used. It is not a table of fixed correction angles for every cue, nor does it describe the whole curve.

Theoretical paper · 김형찬 (Hyeong-Chan Kim)

Motions of a Billiard ball After a cue Stroke ↗

New Physics: Sae Mulli 72, 208–223 (2022) · DOI 10.3938/NPSM.72.208

What this source explains: Analyzes the launch speed, spin and squirt of the ball, taking into account the cue–ball impact and the flexibility of the cue.

Limits: This is a study of a cue impact model. It is not an experiment that proves a particular named stroke is better or that every real shot succeeds.

Educational material · David Alciatore (Dr. Dave)

Squirt, Swerve, and Throw Effects ↗

Online explanations and demonstrations

What this source explains: Separates how cue ball squirt and swerve and object ball throw affect aiming.

Limits: This is pool (pocket billiards) teaching material. Use it to understand the directions, and check the amounts on your own equipment and layouts.

Experimental and theoretical paper · Antonio Doménech-Carbó

Independent friction-restitution description of billiard ball collisions ↗

Mechanics Research Communications 131, 104149 (2023) · DOI 10.1016/j.mechrescom.2023.104149

What this source explains: Separates ball-to-ball friction and restitution from the process of reaching pure rolling after the collision to explain speed, spin and separation direction.

Limits: The experiments with several spheres, billiard balls included, were done on a PVC surface. The measured values cannot be used as-is as corrections for billiard cloth.