A warning track in baseball is a wide strip of dirt that runs along the wall or fence that surrounds the field. A fielder who steps from the grass or artificial turf and onto the dirt surface of the track should notice the different surface underfoot and know that he or she is approaching the wall, even without looking in that direction. The warning track is designed to help prevent injuries that could occur if a fielder who was running to catch a fly ball crashed into a wall — even a padded wall — without warning. Many baseball fields have a warning track along every wall or fence, but others have one only along the outfield wall. Some fields, such as those used by teams in youth, high school or recreational leagues, might not have a warning track at all.
In addition to increasing safety, the track also helps outfielders to better time jumping catches. Many outfielders will track fly balls by looking over their shoulders and therefore will not see that they are quickly approaching the wall. Therefore, they will use their first step onto the track as an indicator to help them know when to jump so that they can reach over the wall and catch what would otherwise be a home run. The warning track frees up a fielder’s field of vision to track the ball rather than having to look and see where the wall is. If the fielder had to take his or her eyes off the ball and look at the wall, he or she might be unable to locate the ball again and therefore would be unable to catch it before it lands.
There is no set distance that a warning track must be. A general rule that is used at many fields is that the track should be about the width of three running steps, which is considered to be enough warning for a fielder. In most major league ballparks, the track is about 15 or 20 feet (about 4.6 to 6.1 m) wide. At other levels of baseball, it might be 6 or 10 feet (1.8 or 3.0 m) wide or some other width within a similar range.
The first use of a warning track came at New York's original Yankee Stadium, which opened in 1923 and was used until 2008. The red cinder track that ran the entire perimeter of the baseball field was originally intended to serve as a running surface for track and field events. Players began to realize that once they hit the cinder track, they were approaching the wall. The warning track was born and began to be included in all baseball parks throughout the major leagues.