Cheat Codes:

Enter these codes at the versus screen. 
More Time After Each Play: 
SQUARE, TRIANGLE, TRIANGLE, CIRCLE, CIRCLE, CIRCLE, LEFT. 

Big Heads: SQUARE, SQUARE, RIGHT. 

Tiny Heads: SQUARE, SQUARE, LEFT. 

Max Out Batting: SQUARE, SQUARE, SQUARE, LEFT. 

Max Out Power: TRIANGLE, TRIANGLE, TRIANGLE, LEFT. 

Unlimited Turbo: 
SQUARE, SQUARE, SQUARE, SQUARE, TRIANGLE, TRIANGLE, 
TRIANGLE, TRIANGLE, CIRCLE, CIRCLE, CIRCLE, CIRCLE, DOWN 

Softball Mode: 
SQUARE, SQUARE, TRIANGLE, TRIANGLE, TRIANGLE, TRIANGLE, 
CIRCLE, CIRCLE, DOWN. 

Ball Is Rubber: 
SQUARE, SQUARE, TRIANGLE, TRIANGLE, TRIANGLE, TRIANGLE, 
CIRCLE, CIRCLE, UP. 

Max Out Speed: CIRCLE, CIRCLE, CIRCLE, LEFT. 

Fantasy Teams and Stadiums :
At the Title Screen or the Main Menu press TRIANGLE, SQUARE, R1 to unlock all 
Fantasy Teams and Fantasy Stadiums.

Lions team:
Hit a home run at Comerica park with the Tigers.

Sub Zero team:
Hit a home run at Midway Park.

Bobblehead team:
Hit ten home runs in a game.

Eagles team:
Get walked three times in one game. To do this easily requires two controllers. 
Use controller two, choose any pitch, but throw a ball.

Scorpion team:
Hit a home run with Sub Zero at Midway Park.

Atlantis stadium:
Hit a home run at Right Field in SBC (San Francisco) 

Coliseum stadium:
Hit a home run at Fenway (Boston Red Sox)

Empire stadium:
Hit a home run at Yankee Stadium (New York Yankees) 

Forbidden stadium:
Hit a home run at Pet Co (San Diego Padres) 

Midway stadium:
Hit a home run at Wrigley Field (Chicago Cubs)

Monument stadium:
Hit a home run at Citzen's Bank (Philadelphia Phillies) 

Rocket Park stadium:
Hit a home run at Minute Made Park (Houston Astros) 

Fantasy team equivalents:
The following is a list of Fantasy teams and the real teams that each corresponds 
to.

Lions: Houston
Horse: Philadelphia
Pinto: Atlanta
Eagles: St. Louis
Gladiators: Boston
Bobble Head: Toronto
Dolphins: Florida
Scorpion: Arizona
Sub-Zero: Seattle
Evil Clowns: NY Yankees
Minotaur: San Francisco
Alien: Minnesota
Casey: Chicago Cubs 

Easy home runs:
Press power swing (Square + L3). This works well in the homerun derby.

To hit very far (about 800 feet), press Up + Turbo + Power Swing at the exact 
correct moment to crush the wall. It is basically luck, but it works.