Baseball Field - Foul Poles

Foul Poles

The purpose of the foul poles is to help the umpire judge whether a fly ball hit above the fence line is foul (out of play) or fair (a home run). The poles are a vertical extension of the foul lines. Both objects are used to determine whether a ball is foul or fair. The outer edge of the foul lines and foul poles define foul territory and both the lines and the poles themselves are actually within fair territory (in sharp contrast to football and basketball where the side and end lines are considered "out of bounds" instead of inbounds).

Prior to 1920, the foul lines extended indefinitely; a batter was awarded a home run only if a fly ball over the fence landed in fair territory, or was fair "when last seen" by the umpire. Under the current rule, a batted ball that goes out of play in flight is judged fair or foul at the point it clears the fence. Thus, a fly ball hitting a foul pole above the top of the outfield fence is a home run, regardless of where the ball goes after striking this pole, and a fly ball clearing the fence on the fair side of the pole is a home run regardless of where it lands.

Foul poles are typically much higher than the top of the outfield fence, and often have a narrow screen running along the fair side of the pole to further aid the umpire's judgment. It can still be a difficult call, especially in ballparks with no outfield stands behind the poles to provide perspective. Wrigley Field is notorious for arguments over long, curving flies down a foul line (most notably in left field) that sail higher than the foul pole. At PETCO Park, there is no foul pole in left field; the pole's function is served by a yellow metal strip along the corner of the Western Metal Supply Co. building.