Also, until approximately that time, the ball had to not only go over the fence in fair territory, but to land in the bleachers in fair territory or to still be visibly fair when disappearing behind a wall. The rule stipulated "fair when last seen" by the umpires. Photos from that era in ballparks, such as the Polo Grounds and Yankee Stadium, show ropes strung from the foul poles to the back of the bleachers, or a second "foul pole" at the back of the bleachers, in a straight line with the foul line, as a visual aid for the umpire. Ballparks still use a visual aid much like the ropes; a net or screen attached to the foul poles on the fair side has replaced ropes. As with American football, where a touchdown once required a literal "touch down" of the ball in the end zone but now only requires the "breaking of the [vertical] plane" of the goal line, in baseball the ball need only "break the plane" of the fence in fair territory (unless the ball is caught by a player who is in play, in which case the batter is called out).