Baseball Stars Cheats (Nes)

Enter the Team Select mode (fast team, good hitting, etc.) then press DOWN, RIGHT, LEFT,
  DOWN, DOWN, RIGHT. Now the screen will say "When isn't it?" Type "When it is." and then
  finish it. Go to VIEW YOUR TEAM and then your will see that your team is ridiculously
powerful.

Go to the MAKE TEAM option on the main menu. Once there, move the control pad in the
  following directions: DOWN, RIGHT, LEFT, DOWN, DOWN, RIGHT, UP, UP, DOWN, UP,
  DOWN, UP. Your controller should be highlighting Veterans. Push A to enter. The message
given
  should be "WHAT IS A WREN?". Delete this and enter "A BIRD." Be sure to remember the
period.

  Press Start so it will accept this. You will be presented with another message saying
"WHEN ISN'T
  IT?". Delete this and enter "WHEN IT IS." As before, remember the period. Put WHEN on
the first
  line and IT IS. on the second line and you will be able to give your team another name.
If you put
  WHEN IT on the first line and IS. on the second line this will still work, but you'll
have to have
  WHEN IT IS. as your team's name. The team you will be given will be no more powerful
than other
  created teams, but all the members will be female (that saves about $100,000 right
there).