A legal slide for a high school runner on a force play (known as the “force play slide rule”) includes either sliding directly into the base or sliding to the side of the base so as to avoid a fielder. On a force play the runner cannot slide to the side of the base with the intent of contacting or hindering the fielder. The runner also cannot carry out a “pop up slide” (using momentum into the base to quickly stand up after the slide) during a force out. This is also an illegal slide. When there is an illegal slide on a force play, the runner is out and so is the batter-runner (or in some cases it will be another runner who would have been the more likely second out).
On a tag play (not a force out), the runner is permitted to slide to the same side of the base the fielder is on, as long as the runner is trying to reach the base safely and he is within reach of the base with his hand or foot. Additionally, if the base is second or third, the runner is not permitted to go beyond the base, going out of reach of it, and contact or hinder a fielder.
[OBR: a slide into the fielder is permitted as long as the runner is able to (and attempts to) reach and stay on the base, and/or the fielder moves into the path of a legal slide. The restriction of being able to stay on the base is only if the base cannot be overrun (second and third).]