"A key feature of bleachers is that they are typically uncovered and unprotected from the sun; thus the wooden seats were "bleached by the sun." The term "bleachers" used in this sense can be traced back to at least 1889. The Dickson Baseball Dictionary states that the open seating area was called the "bleaching boards", as early as 1877. Dickson lists as a secondary definition the fans sitting in them. By the early 1900s, the term "bleachers" was being used for both the seating area and its inhabitants."
Bleacher Bum: A frequenter to baseball games who chooses to sit in the cheap seats, ones without backrests. The phrase is most recognizable with fans of the Chicago Cubs. These fans are arguably considered to be the loudest, rowdiest, and most obnoxious fans in organized baseball. It is not uncommon for a bleacher bum to yell and curse at opposing team's outfielders, perhaps even throwing them a beer shower when the opportunity presents itself. The male bleacher bums tend to not wear shirts, even if the temperatures are highly unfavorable. "
In modern usage the term "bleachers" almost always refers to just the seating area, and those sitting there may be called "bleacher fans", or "bleacherites". Terms such as Chicago's "bleacher bums", or Yankee Stadium's Bleacher Creatures are also used.
Thought I would have a little fun in processing this on Efex. Instead of the ordinary process I used what they call a "bleach" mode. It did darken it, but being its a night shot I thought it would be fun to put more emphasis on that.
Its great fun to sit in the bleachers on a warm summer night. That end of the field is "awash" in beer. Literally.(If you look closely you will see a cup of beer.)