NFL GameDay '99 cheats and cheat codes for Playstation

Cheat Codes
Go to the options screen and select the "Easter Eggs" option.
Then, enter any of the codes bellow:

Code - Result
WEAK - Quick fatigue
TELE TUMMY - Televisions in players' stomachs
SWIMMERS - Swim move juiced
STICKEM - Receivers catch better
STEEL LEG - Longer field goals
STAMINA - Juiced endurance
SPORTS - All players have last name from credits
SLIDESHOW - See cheerleaders after a game
ROCKET MAN - Ball carrier has speed bursts
RED ZONE -  Player named afte developers
PUPPETS - Players have red string attached to head
PRIME TIME - CPU makes big plays
PRESIDENTS - Players named after Presidents
POP WARNER - Tiny, fast players
PLAYING CARDS or FLAT LAND - Flat players
MIND READER - CPU knows your play
ITS IN THE FPS - Scrambled frame rate
INVISIBLE - Invisible players
HOT SHOT - CPU player celebrates in the open field
HOOPS - Players named after basketball players
HANGTIME - Longer and higher punts
HAMSTRUNG - More hamstring injuries
GRUDGE MATCH - Red redzones, checkered touchdown area, invisible field goals
GD CHALLENGE - Extra difficulty level
FLEA CIRCUS - Small players
EVEN TEAMS - All players are equal
EURO LEAGUE - All players have European last names
EGG HEAD - Zero stamina and more fatigue injuries
DAVIS - Faster and stronger running back
CREDITS - Watch the credits
CPU STUFFS - CPU offensive line has super strength and speed
CPU SCORES - CPU players are faster
CON MAN - CPU hides pass coverage
COFFEE BREAK - Speed juiced
BUNYON - Giant players
BOBO - All players' last names are BOBO
BLINDERS - Disable penalties
BIG HITS - Harder tackles
BIG BALLS - Big football

Bonus teams
Press Circle at the team selection scree to select different 
Superbowl and All-Star teams.

Onside kick
To do a short kick that will bounce back (while the returning team is
not ready) just push the X button, when the bar is at its lowest.