Type of stadium construction popular in the United States from the late 1950's to about 1980. (As PeterPan points out, there is a non-American version as well; I'll focus on the American multipurpose stadium in this WU.)

As the National Football League's popularity grew in the 1950's (culminating in the rise of the rival American Football League in the early '60s, eventually itself absorbed by the NFL), and baseball teams started moving (leading to baseball itself expanding), cities with major league franchises in both sports needed 45,000-60,000 seat stadia for each sport. Of course, constructing two new stadia was a very quick way to bankrupt your city treasury and enrage the taxpayers. Trying to fit one sport's field into the other didn't work all that well, either; most originally-baseball stadia couldn't fit a 360 ft x 160 ft (120 yards x 53 yards, 1 foot) rectangle into the field, and trying to shoehorn a baseball field's variable dimensions into what a football stadium would allow made for abominations like a 250-foot left-field wall (and a 440-foot right-center power alley to compensate) at the Los Angeles Coliseum before the Dodgers left for Chavez Ravine.

The solution came out of Washington, oddly enough. RFK Stadium, opened in October 1961, was the nation's first true "multipurpose" stadium; acceptable dimensions for both baseball and football were achieved by first laying out a baseball field, then arcing the outfield wall to allow for a full-size football field to be laid in with one sideline either laid along or just slightly deflected from one foul line.

Of course, a sacrifice had to be made, and the fans' sight lines were that sacrifice. On the football sideline opposite the one that coincided with the baseball foul line, a huge dead corner existed, and the fans were far from the field. In some stadia, temporary stands would be set up in this corner after baseball season was over, but this was still much less than optimal. Don't even think about the sight lines from the upper deck in this corner without binoculars. For baseball, these stadia generally contained symmetrical fields, often with Astroturf to allow the greater wear and tear of two sports on the surface, and were almost always soulless, enclosed bowls with no view of the surrounding city or quirky ground rules to make outfield play interesting.

RFK Stadium was the first, but many such stadia followed. Some that come to mind quickly:

The observant reader may note that most of these stadia are long gone. This can be directly traced to the 1992 opening of Oriole Park at Camden Yards in Baltimore. This retro baseball-only park with modern amenities quickly became the gold standard and touched off a massive single-sport construction boom in baseball. Desire for parity and luxury boxes caused football teams to go on their own construction binge shortly thereafter.

The days of the multipurpose stadium are mostly done now, and very few sports fans are sad to see them go.

* Memorial Stadium actually pre-dated RFK, but was originally constructed for football, and had a greatly reduced capacity in its minor league baseball configuration; subsequent expansions made it usable for the major league Orioles, but it wasn't a true multipurpose bowl-type stadium.