In addition to the centre, pyramid, and billiard spots on the billiard table, there is a fourth imaginary spot, also on the central line of the table and (for ivory balls) 24½ inches above the baulk line. From this spot there are two imaginary lines which proceed transversely to within 15 inches of the two middle pockets, and a plain half-ball contact from hand, played into a middle pocket when the object ball is on either of these imaginary lines, has the effect, if accurate both as to contact and strength, of bringing the object ball back to the point from which it started. Better one-ball practice than this can scarcely be imagined.
The eye is trained to the half-ball angle; carefulness as to exact aim is inculcated; and the right strength to adopt for half-ball middle pocket play soon becomes instinctive.
If, however, the red ball comes to rest below this line a fuller than half-ball contact must be employed, and if it comes to rest a little higher up the table the contact must be proportionately finer, as the red ball has either to be kept travelling parallel with the side cushions or so driven or cut that it shall seek the mid-longitudinal section of the table on its return rather than the cushions of the side section from which it started. On the other hand, when the red ball is near to a middle pocket and quite half-way up the table, a better stroke than seeking to cut it on to the top cushion by means of a fine stroke is to play rather fully on to it and so drive it towards the centre of the table by way of both the side and the top cushion.
When the red ball is near the centre line, but a shade too high up for the plain half-ball contact, the stroke may still be made half-ball by playing with side at the same strength and aiming a trifle fuller than half-ball. (This class of shot is also extremely useful under similar circumstances with the cross loser at the top of the table, or with the loser from an inch or so away from the middle pocket off the red ball on the billiard spot. But when the red ball is more than slightly out of the range of plain half-ball middle-pocket play from baulk, it is much better to discard the idea either of the side stroke or of a forcing stroke into the middle pocket and to turn immediately to the loser into a top pocket instead.
The real difficulty of middle pocket play is not, however, to be found in the accurate half-ball contact and strength, but in the manipulation of those run-throughs below the halfball line, and those fine cuts above it to which reference has already been made, and a good general rule for the learner to bear in mind is that the run-throughs should always be played thicker than they seem to need and the fine strokes finer. This is, indeed, a sound billiard rule at any part of the table, and it will be found that whereas amateurs nearly always break down by under-doing this rule, professionals, when they break down, are seen to have slightly overdone it.
Although we may seem to have suggested that below the two two-feet diagonal lines to the middle pocket all strokes must be full, and above them fine, there are two or three exceptions to this general rule which deserve to be noted.
Sometimes the red ball, although below the line, is in a position where either a half-ball contact on one side, or a run-through on the other will find one pocket or the other whilst still giving good direction towards the top cushion to the object ball, and either the half-ball contact or a fine contact may be employed with gentle strength when it is only intended to guide the red ball towards the centre line without invoking the aid of the top cushion at all. These last two strokes, however, are amongst the exceptions to ordinary red ball middle pocket play and come rather under the head of finesse than of general straightforward play.
Ordinarily speaking, middle pocket play resolves itself into the three main elements of cue-ball positioning in the 1), of the degree of object-ball contact, and of the strength employed. After a time the positioning of the cue ball in the D becomes almost instinctive, but at first the best plan is to place it for the half-ball angle and then to glance from the half ball contact point (which is midway between the edge and the centre of the ball) to the top cushion. It will instantly be seen whether this part of the top cushion is a desirable point for the object ball to rebound from, and if it is not the positioning of the cue ball in the D must be made fuller and the red ball must be played upon either finer or fuller from that positioning, according as to whether it is designed to cut or drive the red ball to the desired part of the top cushion. Here it is that the important consideration of strength has to be taken into account, for the strength to be applied to a finer or fuller than half-ball contact must necessarily be greater or less respectively than that employed for a half-ball shot in order to impart the same amount of travel to the red ball. Each eighth-inch divergence of contact sensibly affects the run of both balls, which is practically identical at half-ball. But with finer than half-ball contacts the cue ball travels farther and the object ball less, and with fuller than half-ball contacts the cue ball travels less and the object ball farther. Thus it may even be necessary to send the cue ball two table-lengths in order to cut the red ball with extreme fineness only a few inches, and to send the object ball two table-lengths whilst the cue ball, taking the object ball almost dead full at near range, only travels a foot or so.
Although not directly connected with the subject of red ball control for pocket play, this feature of reduced strength for fuller than half-ball contacts may well be considered in its relation to slow screw shots at near range as in top-of-the-table play. Many amateurs are sometimes surprised to note with what extremely gentle strength screw strokes, whether for cannoning or losing hazard purposes, are made by professionals at the head of the table. Accustomed to play almost all screw strokes with force, some amateurs regard these effects with admiration not unmixed with awe. The solution is really very simple. It is the fuller contact, combined with lower cueing, that enables the artist to accomplish anything between a straight draw-back and a half-ball screw with gentleness combined with effect.