Activities Sports & Athletics Aim Primer 5: Contact Point And Half Ball Line Share PINTEREST Email Print Sports & Athletics Billiards Shots & Strokes Equipment Baseball Basketball Bicycling Bodybuilding Bowling Boxing Car Racing Cheerleading Cricket Extreme Sports Football Golf Gymnastics Ice Hockey Martial Arts Professional Wrestling Skateboarding Skating Paintball Soccer Swimming & Diving Table Tennis Tennis Track & Field Volleyball Other Activities Learn More By Matthew Sherman Matthew Sherman is an experienced pool and billiards instructor and the author of "Picture Yourself Shooting Pool." our editorial process Matthew Sherman Updated June 19, 2017 01 of 04 Aim Primer 5: Contact Point And Half Ball Line From behind the cue ball, all things are possible using this aim primer. Photo (c) Matt Sherman, licensed to About.com, Inc. Continuing our Aim Primer from behind the cue ball with more information on dividing balls and the contact point. The Stable Contact Point Regardless of cue ball direction of travel, and discounting concepts of collision-induced throw and etc., the cue ball can come from any direction yet strike the 2-ball on its contact point to sink it. The key thought is that the cue ball is moved to hit the contact point, which would remain unmoved regardless of where the cue ball began. Any degree of cut angle may thus be made successfully from 0 degrees (a full hit) up to 90 degrees (the thinnest hit possible). CAUTION: The ball numbers on object balls make convenient contact point markers for practice. Turn an aimed ball in place so that one number rests at the contact point (as far as possible from the pocket along its equator; the opposite number on the ball's equator will be at the point closet to the pocket opening). CAUTION: All pool aiming is done backwards from the pocket, finding the aim line first before then deriving the shot line from its relationship to the pocket aim line. Next Page: Half Ball Aim 02 of 04 The Full Line - Understanding This Key Concept The full line is where many fine billiards players stand to consider the upcoming shot. Illustration (c) Matt Sherman, licensed to About.com, Inc. Half Ball Fractional Aim From The Full Line The diagram illustrates the cue ball starting position used throughout this aim manual. It also represents a common fractional aim choice, called a half ball hit. The cue ball has been placed with a "C" directly opposite Diamond D and a spot a few inches closer to the 2-ball then the distance halfway between Diamonds C and E at the top of the diagram. The centerline of the three gray lines shown is called "the full line" and runs between the bases of the balls. From the player's perspective, if the cue ball were to be stroked along the full line it will impact the 2-ball as a "full hit". With eyes watching from behind the cue ball in the stance, the cue ball will fully eclipse the sphere of the 2-ball at impact, as the disc of the moon in the sky fully eclipses the equal disc of the sun when they align perfectly. CAUTION: The full line is vital to know since with few exceptions, most professional players and skilled amateurs stand along the extended full line to begin aiming most cut shots. The two lines parallel to the full line touch the "sides" of the two balls and provide two "edges". Spherical objects have but one continuous edge in three-dimensional space, but for sighting and aiming the player watching from behind the cue ball sees right and left edges of the ball, just as a full moon appears as a two-dimensional circle in space when earthbound observers cannot see the moon's far side. Ball edges make handy aim reference points. Next page: The Edge Marker 03 of 04 The Edge - Marker For The Half Ball Shot Line The edge of the ball is where the half ball line is derived. Illustration (c) Matt Sherman, licensed to About.com, Inc. Proceeding from the edge of the ball, we continue our look at: The Half Ball Shot Line The position of the balls has remained the same in this diagram as in that on the first page, but a new line, the shot line, has been drawn. The balls and pocket are aligned such that a player who plots a line through the base of the cue ball and along the right edge of the 2-ball (the rightmost edge of the circle of the ball as seen from the stance) can drive the cue ball C to the aim line at G and score the 2-ball. CAUTION: Note how the shot line/cue stick as diagrammed bisects the cue ball for a center ball hit. Center ball is used for all shots in this manual. Aiming center ball/base of the cue ball at the edge of an object ball is a "half ball hit", because the cue ball is seen to eclipse one half of the object ball during the stroke as in Diagram 11. Center ball is aimed at the edge of the 2-ball, but cannot actually impact there. Next page: The player's perspective along the edge of the ball. 04 of 04 Half Ball - One Pro Aim Method The half ball hit from the player's perspective near the cloth. Illustration (c) Matt Sherman, licensed to About.com, Inc. The illustration shows a half ball hit as viewed from behind the shot. The blue box represents where center ball was aimed at the yellow ball's edge. The cue ball eclipses half its surface. The center of the intersected region of the balls, however, (shown as a red spot in this diagram) is where the balls actually touch. If you can find where the blue box and red spot would go in the illustration on the previous page (a half ball hit seen from above) you understand how center ball is at times aimed to miss the object ball while a glancing blow actually pockets the ball. The red spot denotes the geometric contact point.