Warning track

The warning track is the part of the baseball field that is closest to the wall or fence and is typically made of dirt, instead of grass or artificial turf like most of the field. It runs parallel to the ballpark's wall and looks like a running track. The change of terrain from grass to dirt serves as a "warning" for fielders trying to make a deep catch that they are running out of room, since it is often difficult for the fielder to keep his eye on a fly ball while keeping track of his position relative to the wall.