A double sends the object ball off a cushion and into a pocket. It uses the cushion ideas from post 07 for the ball you hit. This lesson covers the mirror pocket, a quick way to find the cushion point, the pace a double needs and how pace moves the line, the cross double and the cut-back, the double kiss and how to avoid it, a double into the corner, and when a double is worth playing.

Series map. ★ Basics: 01 Cue action and elevation → 02 Aiming and potting → 03 Tip and power → 04 Where the white goes · ★★ Club: 05 Side spin → 06 Cut and side into pockets → 07 Cushions → 08 Doubles (this post) · ★★★ Advanced: 09 Escaping snookers → 10 Multi-ball shots → 11 Safety → 12 Position play · ★★★★ Hard: 13 Break-building → 14 Special shots · Reference: 15 Rules, tactics and practice · ★★★★★ Pro: 16 Cue-ball control.

Learning Outcome

Find the double's line by mirroring the pocket, and check it by proportion.
Give a double enough pace, and allow for the line moving at high pace.
Tell a cross double from a cut-back double, and know the risk in each.
Spot and avoid the double kiss.
Play a double into a corner pocket.
Decide when a double is the right shot.

Chapter 1 — The line

1 · Mirror the pocket

Top view of a red near the top side cushion, a little left of the top middle pocket. A dashed line goes from the red up to a yellow point on the cushion and on towards a mirror pocket above the table. The red's track goes up to that point, comes back down across the table and into the bottom middle pocket, tick. The white sits below the red, on the line

Picture the pocket reflected behind the cushion, the same distance on the other side (the mirror pocket).
The red must go at the mirror pocket. Where that line meets the cushion is the point the red must hit.
Now it is a normal pot at the mirror pocket: find the ghost ball and aim (post 02).

A red that has just been hit is sliding, and a sliding ball comes off a cushion close to the mirror line (post 07).

Trick: check the line from the other end. Stand behind the pocket and look at the cushion point: the red should sit on the reflected line.

2 · Find the cushion point by proportion

A diagram of a double. The red is near the top cushion, the pocket on the far side. The cushion point splits the distance along the cushion in the same ratio as the red's and the pocket's distances from the cushion: here about one fifth of the way

The mirror rule gives a quick check. The cushion point splits the distance along the cushion in the same ratio as the distances from the cushion:

	From the cushion	Along the cushion
red	a = 40 cm	5 cm to the cushion point
pocket	b = 176 cm	22 cm from the cushion point

40 : 176 is the same as 5 : 22. So a red close to the cushion hits it almost straight in front of itself; a red half-way across hits it half-way to the pocket.

3 · Pace: a double is a long pot

Two top views of the same straight double. Power 3: the red comes off the cushion and stops in the middle of the table, cross. Power 4: the red reaches the bottom middle pocket, tick

This red travels about 2.2 m: up to the cushion, then all the way across. The cushion also takes pace off it.

White	Power 3	Power 4	Power 5
straight behind the red (full ball)	stops short ✗	✓	✓
from the left (cut about 35°)	short, and the white went in-off ✗	✓	✓
from the right (cut about 50°)	short ✗	✓	✓

(Each ✓ is with the aim fine-tuned; section 4 shows why power 5 needs it.) Power 4 was enough every time; power 3 never was. The thinner you hit the red, the less pace it gets (post 04), so on a cut double lean towards the firmer side.

4 · Firm doubles come off a little short

Close-up top view of the bottom middle pocket. Two red tracks come down from the top cushion on the same mirror aim. Power 4 arrives 2 cm from the pocket's centre, tick. Power 5 arrives 6 cm to the left, cross

The same mirror aim at two paces (model):

Power	Reaches the far cushion	Result
4	2 cm from the pocket's centre	✓
5	6 cm short of it	✗

At high pace the red comes off the cushion a little short (squarer). At power 5 the aim needed turning about 0.2° to make up for it. So: play doubles at the lowest pace that gets there, and if you must hit hard, aim a touch longer.

Chapter 2 — Cross, cut-back and the kiss

5 · Two ways to play it

Two top views of the same double into the bottom middle pocket, both potted. 1: the white comes from the lower left; after contact it runs right, across the red's path back from the cushion. 2: the white comes from the lower right; after contact it goes up and away to the left, not crossing the red's path

	Cross double (1)	Cut-back double (2)
White comes from	the same side the red comes back to	the other side
After contact the white	runs across the red's path back	goes away from it
Main risk	a kiss: the red hits the white on its way back	a thinner hit, so less pace and a harder line

Neither is "the" right way; it depends on where the white is.

6 · Watch it: a cross double

Power 4, centre ball. The white runs across the red's path but has already gone past before the red comes back.

7 · The double kiss

A red 6 cm off the cushion, hit full: the red reaches the cushion, bounces straight back, and meets the white again before the white has gone anywhere. That second contact is a double kiss: the red goes off line.

Watch out: pace does not fix it. At power 3, 4 and 5 the white met the red twice every time. The white is simply too close.

8 · Change the angle to avoid the kiss

Three top views of the same red near the top side cushion. 1: full ball at power 4: the white and red meet twice, cross. 2: the white comes from 30 degrees to the right at power 5: one contact, the red doubles into the bottom middle pocket, tick. 3: the white comes from 30 degrees to the left at power 5: one contact, the red goes in, tick

Change the angle, so the white moves out of the red's way after the first contact:

	White comes in	Contacts	Result
1	straight (full ball)	2	✗ double kiss
2	30° from the right (cut-back double)	1	✓
3	30° from the left (cross double)	1	✓

A cut needs more pace; here power 5. Before any shot into a nearby cushion, ask: "after the first contact, does the white get out of the way?"

Chapter 3 — More doubles

9 · A double into the corner

Top view of the right half of the table. A red near the top side cushion is doubled off it, down the table into the bottom-right corner pocket, tick. A yellow dot marks the cushion point; the white comes from below left and stops close to where it hit the red

The same mirror idea works for a corner: reflect the corner pocket behind the cushion and send the red at it. Here a red near the top cushion, power 4, aim turned 0.2° from the mirror line (model).

Trick: a corner double comes into the pocket at a slant, so give it the jaws, not the cushion. If the line runs close along the end cushion, it has only about 2 cm of room (post 06).

10 · When to play a double

When the direct pot is blocked or impossible.
When the double is close to straight (the white more or less behind the red, as in picture 1): those are the easiest.
As a "shot to nothing": a miss sends the red back across the table, often to a place that is awkward for your opponent. Check where it goes before you play.

Before you play it, check the white: where does it go at this pace, and is there a pocket or a kiss on its path?

Try it at the table

Drill	Set-up	Look for
Straight double	a red 40 cm off a side cushion, level with the middle pocket; the white behind it	power 4 reaches the opposite middle pocket
Proportion check	the same, the red moved 30 cm towards baulk	find the cushion point by a : b before you get down
Pace ladder	the same double at power 4, then power 5	the firm one comes off a little short
Cross vs cut-back	the white 50 cm left, then 50 cm right of the line	a clean pot both ways, no kiss
Kiss test	a red 6 cm off the cushion, full ball, then from 30°	the full one kisses, the angled one does not
Corner double	a red 30 cm off the top cushion, 60 cm from the end	it drops into the far corner

Cheat-sheet


Line	send the red at the mirror pocket
Check	cushion point splits the distance along in the ratio a : b
Pace	long trip: power 4; firmer comes off a little short
Cross double	the white crosses the red's way back: watch the kiss
Cut-back double	thinner hit, so lean firmer
Double kiss	red close to the cushion, hit full: change the angle
Corner double	mirror the corner pocket; aim for the jaws
Best doubles	close to straight, from close range

What's next

09 · Escaping snookers (對射角). The same mirror, used for the white: hit a ball you cannot see directly, off one, two or three cushions, or with a swerve.

References

WPBSA, Official Rules (2022): table and pocket positions. https://wpbsa.com/rules/
Dr. Dave Alciatore, bank-shot (double) aiming systems and cushion rebound. https://billiards.colostate.edu/
The proportion rule is exact geometry for angle in = angle out. Paces, lines and the kiss come from the physics model used in every post (cushion restitution 0.8, the cushion meeting the ball above its centre). Real cushions differ table to table; check your table with the drills.