Carom billiards
When straight rail was first invented there was no restriction on the way points were scored. However, the technique of crotching, meaning to have two balls right next to each other on the area of one of the table's four corners where the rails meet—the crotch—made scoring a lot easier. This resulted in an 1862 rule which allowed only three counts before at least one ball had to be sent away from the corner in order to legally score another point. Techniques continued to develop which increased counts greatly despite the crotching ban. One of these techniques is called "nursing", and made scoring much easier. A "nurse" is a series of shots where the balls are kept very close together, allowing a player to score off of them with very soft strokes without changing their positions much, so the scoring can continue. The most important of these nurse techniques, called the rail nurse, involves nudging the balls down a rail, moving them just a few centimeters on each score and keeping them close together and positioned at the end of each stroke in the same or near the same arrangement so that the rail nurse can be repeated.