Bridge, stance and a straight stroke: cueing basics

Most advice about the bridge, the stance and the stroke is handed down as habit. Each piece has a simple geometric purpose, which is to keep the cue travelling along the line you aimed. This post puts numbers on why that matters, and separates the numbers, which can be checked, from the coaching guidelines, which are rules of thumb that vary from player to player.

A small angle becomes a big miss

If the cue ball sets off at an angle e away from the line you aimed along, then after travelling a distance d it is off that line by

For small angles tan(e) is close to e in radians, so the miss grows in a straight line with distance. A ball has a diameter of 57.15 mm (2¼ inches), which gives a yardstick for how much sideways error a shot can take. The table below uses 0.5 m, 1 m and 2 m, which are a short shot, a medium shot and a long shot on a full-size table (a 9-foot table is about 2.54 m long on the playing surface).

Read the table against the ball. One degree over a metre is 17.5 mm, about 31% of a ball diameter. One degree over 2 m is 34.9 mm, or 61%. Two degrees over 2 m is 69.8 mm, more than a whole ball. A shift of half a diameter (28.6 mm) at the object ball needs only 1.64 m at 1 degree, or 0.82 m at 2 degrees.

The practical reading is that distance multiplies every flaw. A 1 degree wobble is harmless on a shot of 30 cm and costly on a full-length one. And because the object ball then has to travel to the pocket, the error you put in at the cue is not the last one the shot has to survive.

The bridge: a pivot you can shorten

The bridge hand is the rear support for the front of the cue, so it sets the line near the cue ball. Two geometric facts follow:

• The cue is guided over a short length at the front, so a small sideways slip at the bridge changes the line before the tip has gone far. Keeping the bridge firm and the cue sliding in a groove is about stopping that slip.
• The farther the bridge is from the cue ball, the more of the cue's length is unsupported ahead of your hand, and the more room there is for the tip to drift sideways as the cue moves forward.

A common coaching guideline is to place the bridge hand roughly 15 to 25 cm (6 to 10 inches) behind the cue ball for an ordinary shot, shorter for a delicate one and longer when you need a long, free stroke. This is a starting point rather than a rule, and a player with long arms or an unusual grip may settle elsewhere. What can be said firmly is the direction: a shorter bridge gives the tip less distance to wander, and a longer bridge gives the stroke more room.

The stance: putting the eyes on the line

The stance is there so that your eyes, your chin and the cue lie in one vertical plane with the line of the shot. If your head sits to one side of the cue, you look at the line from an angle, and the cue may appear straight while it points a degree or two away. The usual guidelines are these:

1. Chin low and over the cue, so that the cue passes beneath your gaze and the sighting line and the cue line coincide.
2. Feet about shoulder-width apart, with the body turned so the cue arm swings freely past the hip.
3. Back forearm hanging close to vertical at the moment of contact, so the cue moves in a plane instead of arcing sideways.
4. Stay down after the shot, because lifting early is a way of twisting the cue off its line before the tip has left the ball.

None of these is a law. They are the arrangement that most players find keeps the cue on one line most often, and each can be checked by sighting along the cue with a friend or a phone camera.

A straight stroke

The stroke is where the line is kept or lost. The cue should move back and forward along the aimed line, with only the forearm swinging if the upper arm is still. A useful drill is to lay the cue along a table line, such as the long string, and play a few practice strokes without a ball, watching the tip. Then use the numbers above as a target: on a 1 m shot, an error of 1 degree in the cue's line puts the cue ball 17.5 mm off its aimed path at the object ball, so that is the size of slip the stroke has to stay under.

What carries over to a phone

A phone game is aimed by touch, not with a cue, so there is no bridge or stance to get wrong. What does carry over is the line of aim and the geometry behind it. Placing the line through the ghost ball is the same task described in aiming with the ghost ball, and the same distance rule applies to any line you set: a small error at the start is a larger error at the far end. After contact, the cue ball's path is covered in the 30-degree rule, and the object ball's small departure from the line of centres in throw and overcut.

The Play listing for 8balls says you can adjust your aim, shot power and cue-ball spin, and switch between overhead and aiming views. A long shot is a good test of the table above: set the line as carefully as you can, and compare where the cue ball goes with where you meant it to go.