There is a nearly universal law when it comes to ballpark evolution: Playing surfaces are shrinking.

Major-league parks in the modern era, kick-started by the opening of Camden Yards 30 years ago, generally feature less square footage than the MLB homes that preceded them.

And teams have tinkered with stadiums throughout baseball history, adjusting dimensions that weren't as favorable as hoped. Outfield fences have mostly been moved closer to home plate to encourage more offense.

But the Baltimore Orioles announced last week that they would buck the trend and move back the left-field fence at Camden Yards.

General manager Mike Elias told reporters that when he was brought in to rebuild the franchise more than three years ago, he was charged with taking a fresh look at everything, and it turns out that included the ballpark. He felt it had become an impediment to the Orioles.

"It is being done with the goal in mind of bringing the playing conditions more toward the league norm," Elias said last week of the change. "Since inception, it's been an extreme park for home runs. That has only grown as the style of play in the major leagues has evolved."


The space race

The first steel-and-concrete stadiums that emerged in the early 20th century, now known as "jewel-box parks," averaged 416 feet from home plate to center field, according to data from the Clem's Baseball's stadium database. The distance averaged 407 feet in stadiums built from 1923-91 and 403 feet in the new, Camden-era ballparks.

The average power-alley distances haven't changed as much - the average distance to left-center in jewel-box era parks was 377 feet, remained the same for stadiums built in the middle era, and ticked down to 373 feet in stadiums built since 1991. (The right-field gaps average 367, 372, and 374, respectively).

The field dimensions of yore that made it nearly impossible for many batters to hit a ball out of the park have gone extinct. The days of distances like 483 feet to center field at the Polo Grounds, or the 457-foot, left-center power alley at the original Yankee Stadium, are over. Overall, the gap-to-gap square footage has generally fallen.

It's foul territory, though, where ballparks have shrunk dramatically. Since 1992, the newest parks average 22,700 square feet of foul territory, compared to 27,900 in those parks built between 1923-91 and 28,500 square feet in the jewel-box era. That squeeze - 19% and 21% declines - reduces foul-outs and gives batters more lives at the plate.

And after stadiums open, their outfield dimensions usually contract.

Long since demolished stadiums like Shibe Park, Sportsman's Park, Tiger Stadium, and the original Comiskey Park and Yankee Stadium brought portions of their fences in. Fenway Park with its right-field bullpens and Wrigley Field have also reduced depths since their debuts. Dodger Stadium, the gem of the mid-century era, never changed its fences, but it did move home plate 10 feet forward in 1969. The Dodgers also eroded foul territory over the years with multiple seating additions.

Of the 23 modern-era parks, 10 have moved in at least part of their fences, and two, the Mets' Citi Field and the Marlins' loanDepot Park, moved in significant portions of their outfield walls twice. Three ballparks have reduced fence distance by more than 20 feet in certain areas of the outfield: Citi Field, loanDepot Park, and Comerica Park in Detroit.

Only two venues have gone in the opposite direction. Citizens Bank Park in Philadelphia pushed back its left-field wall a few feet in 2006, according to media reports and an analysis of the ballpark diagrams at Clem's Baseball. Coors Field in Denver also raised a portion of its right-field wall.

But just as the Orioles broke with convention 30 years ago by building an asymmetrical ballpark that fit within the constraints of city streets and an old railroad depot - a decision that sparked the greatest stadium boom and design change since Shibe Park opened in 1909 - they're doing it again with this latest project.