In baseball, a slide is the action of a player, acting as a baserunner, who drops his body to the ground once he is very close to the base he is approaching and slides along the ground to reach the base. Sliding is widely considered to be an essential component of baserunning in both youth and professional baseball, though not precisely for the same reason.
A baserunner may slide into a base in a number of different ways and for a number of perceived reasons, including to avoid a tag out, to avoid overrunning the base, and to interfere or avoid contact with the defensive player protecting the base. Adult amateur players should determine whether they will benefit by sliding in a particular game situation, and whether an increased risk of injury will make a slide worthwhile.
There are many different ways to slide, involving different ways of attempting to avoid the tag, reaching to touch the base, and/or trying to contact or avoid collision with the defensive player. Since the defense generally expects a slide, sometimes a baserunner trying to avoid being tagged out will not slide directly towards the base, but rather to a side away from where the ball is coming, and then reach back to touch the base.
Players generally slide feet-first but sometimes also use a head-first technique. Strictly speaking, going headfirst into a base constitutes more of a dive than a slide, but the term "slide" is still commonly used. This alternate method has been used in Major League Baseball at least since the middle-1880s when the innovation was popularized by the St. Louis Browns of the American Association. Yet even in the majors, it remained relatively uncommon until it became popularized by Pete Rose in the 1960s. Headfirst sliding has since become a common practice for various players on all levels of professional baseball, but it is often restricted on the amateur level.
On plays in which the baserunner may be tagged out by the opposing defensive player covering the base, the baserunner's body being down on the ground presents the lowest profile target for the defensive player to tag. This makes it slightly more difficult for the defensive player to apply the tag in time to put out the baserunner.