The Tangent Line is one of the most important things to know regarding position play. Simply defined, the tangent line is the natural direction a sliding cue ball takes after contacting an object ball. If a cue ball is rolling when it contacts an object ball, (topspin) or spinning backwards (Draw) when it contacts an object ball, the cue ball will roll forward or behind the tangent line.
The tangent line is perpendicular to a line drawn through the object ball and cue ball at the point of contact. This is a 90 degree angle from the path of the object ball to the pocket. On all shots the cue ball will travel this path unless it is shot with follow or draw.
Depending on the circumstances you may want to have the cue ball follow this line. If that is the case you need to have the cue ball sliding, not rolling or spinning when it makes contact with the object ball. Depending on the distance between the object and cue ball, you have to adjust your contact point on the cue ball or the hardness of the hit. This takes a lot of trial and error to find the best combination of speed and cue tip location.
In some cases you simply need to hit harder to keep the cue ball sliding over a longer distance. In some shots you need to hit lower on the cue ball so it starts out spinning backwards but has stopped spinning at the moment of contact with the cue ball.Identifying and understanding the tangent line on each and every shot will become a guide to your controlling the cue ball and becoming successful at position play. You can use forward roll or topspin to have the cue ball roll forward of the tangent line, or use a draw stroke to have the cue ball move behind the tangent line.
Learning these techniques and using the tangent line will improve your success at position play. You can adjust your position far more effectively with topspin or draw once you know where that tangent line is. Often this skill is very important to help you avoid scratching or breaking out a cluster of balls. It's all about The tangent line that you want to follow, go over or stay behind with the cue ball. This is a decision to make on every shot.