Warning track

[1]: 18  The change of terrain 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.

[3] Despite the warning track's presence, it is common to see outfielders crash into the wall to make a catch, due to a desire to field the play regardless of the outcome, because they fail to register the warning in time, as they are looking up at the fly ball, or because they do not know how many steps they will have on the track.

[5] In 1949 Major League Baseball formally began requiring a warning track.

[1]: 18  In general it is designed to give fielders three steps of warning before the outfield wall.

[1]: 18, 21 [8] When Major League Baseball instituted the warning track, it was 10 feet (3 m) wide.