(This is today's bit of advice from the book Safety Toolbox.)
Clusters occur when two or more balls are clumped together. A cluster can consist of only two balls, if they mutually interfere with each other. They create problems that often stop a run. To most players they are roadblocks to easy wins.
Sooner or later, they have to be handled. Many players attempt to open up a cluster in the process of pocketing other balls. If it can be done, that allows a run to continue. If the attempt fails, the problem remains. There are advantages and disadvantages to opening them during the early-game or waiting for the mid-game or end-game.
To the intelligent shooter, clusters are opportunities to create problems for your opponent. With your superior safety knowledge and precision ball control, they offer many and varied situations. For you, a cluster is a toy. With a three-ball cluster, you can tickle out one ball and leave two of them still tied up. With a two-ball cluster, you can push one ball out, and send the other to a dead zone while playing a safety. Choices are only limited to your skills and imagination.
8 Ball clustering tactics
Clusters are common immediately following the break. Generally there are two or more groups, a mix of both stripes and solids. In the process of the game, these need to be handled.
Top players will open these up during the run out. Even if the breakout leaves balls in tough positions, they can usually be pocketed. For the regular player, almost all runs end when a cluster has to be faced. Many players leave clusters to the end-game. They are mentally lazy, and don't want to face them until forced to do so by the rules of the game.
Depending on the layout and your opponent's skills, open all but one of the clusters that ties up his ball (see Insurance balls, page 144). While opening your balls out into the middle or near pockets, try to push his into dead zones. (As a matter of standard practice, look for any opportunity to push two or more of his balls together.) In this way, if your opponent gets ahead of you, he must use an inning to open up the cluster.
9 Ball clustering tactics
On the break, two-ball clusters are common, although a three-ball group does happen once in a while. How you play with these clusters depends on the skill level of your opponent. Much of your cluster tactics depend on circumstantial opportunities offered by the table layout and your imagination.
If your opponent is the better player, early in the game create a cluster of two or three balls. This stops any run-out attempts. He might still shoot his way out of it, but you force him to do more work (always a good thing). Concentrate on tying up the 6, 7, and 8 balls. Early in the game, you can use an illegal shot to do this.
If evenly matched, set him up to face clusters with the 4, 5, and 6 balls. This gives you a chance to manage the table at the mid-game. After he is forced to wade through the mess, you can manage circumstances to ensure the win. If you are the superior player, tie balls up for him around the 6, 7, and 8 to ensure a game win.