In baseball, a home run that is hit an exceptionally long distance from the field of play.
The term "tape measure" originated from a home run hit by Mickey Mantle in 1956. The ball's distance was measured and on the day following the baseball game Mantle appeared in the newspaper holding a tape measure.
The longest home run ever estimated is a subject of much debate. The Guinness Book of World Records lists Micky Mantle's 634-ft. home run hit against the Detriot Tigers in 1960. However, home runs can only be measured conceptually, due to the fact that most balls leaving the field of play run into obstacles or barriers that prevent them from flying their actual distance.
The Home Run Derby, part of the exhibition entertainment during the week of the MLB All-Star Game, is centered around the league's top home-run hitters competing in a contest for the most home runs with a specific number of outs. This type of exhibition is an example of fan fascination with tape-measure home runs.