Blernsball is a game from the Futurama fictional universe. It is a "jazzed up" version of baseball, which was "as boring as mom and apple pie." Steroid injections are mandatory for all players. Leela was the first woman to play blernsball, but was only a gimmick to draw in fans. Players (at least those on the New New York Mets team) have fractions on their jerseys because all the natural numbers have been retired.

Blernsball Play
Although similar in play to baseball, many new rules have been integrated into the game. These include:

The ball is attached to the field by an elastic tether, though powerful hits have been known to break it (a billboard just beyond the reach of the tether triggers an "automatic win" if the ball enters a small hole in the centre, and previous balls have been known to escape from Earth's atmosphere). 
There is a mandatory "steroid injection" rule for players, but apparently Leela was exempt from the rule. 
If the ball goes into a small hole in the center of the field (a 'third ball lock'), "Multiball" is initiated. At this time dozens of balls are shot at high speeds into the field, sending the players screaming. 
Relief pitchers are conveyed from the bullpen to the pitcher's mound by means of a giant tarantula. (A notable exception was during Leela's stint as a relief pitcher with the New New York Mets, where she typically remained in the dugout). 
A player may circle the bases on a hovering motorbike in some cases, causing the bases to explode. 
Traditions of the game include aluminum bats and the 7th inning grope. 
As revealed in a DVD audio commentary track, concerning the rules behind the sport, the writers apparently try to keep the full rules of Blernsball just out of the realm of understandability.


List of blernsball teams
The Boston Poindexters 
The Mars Greenskins 
The New New York Mets 
The New New York Yankees 
The Pituitary Giants 
The Swedish Meatballs 

Trivia
The name 'blerns' originates from an early period in the show's run. The staff were heavily swamped, and working 7 days a week. During this period, scheduling was done on an 8 day week, with 'blernsday' being the additional day. 
During the credits of "Bender Should Not Be Allowed On TV", Leela mentions "Blernsday Night Blernsball" during the cast's rendition of the Black Flag song "TV Party". 
The current worst blernsball player of all time is Turanga Leela, who replaced Hank Aaron the XXIV. 
There was once a blernsball Robot League, mentioned by Bender in "Fear of a Bot Planet". This is in reference to the great Negro leagues of the 30's and 40's and continues the series' subtle theme of human/robot relations. 
The '3rd ball lock' and 'multiball' plays are references to pinball machines. 
The motorcycle that has been used to circle the bases is a TRON Light Cycle.