Go to the Cheat Code screen and enter the following phrases to unlock the corresponding cheat:

989 SPORTS: Players named after 989 team.
ALL BOBO: All players will have the last name "Bobo."
BASKETBALL: Players will be named after NBA superstars.
BIG PIG: Make the football large.
CREDITS: Watch the game's creits.
ENDURANCE: Give your players more endurance.
EURO LEAGUE: Players will be named after NFL Europe stars.
FASHION SHOW: Cheerleaders' pictures will appear after the game.
FATIGUE: This will reduce your players' fatigue.
GRUDGE MATCH: This unlocks the GameDay stadium.
LINE BUSTER: This will improve your defensive line.
OVAL OFFICE: Players will be named after Presidents of the United States of America.
PENCILS: Makes all players thin and tall.
POP WARNER: Players float above the field.
SUPER FOOT: This makes your running back better.
TINY: Makes all players big and fat.