Glitch Team - In 1p mode, first, select the National All-Stars. Then select to play American league all stars. after the game with the American league, you will play the glitch team. Beware, this game will be an ass kicking. If your NES or emulator last through the game, you can play a better glitch team. Watch out for the 150 mile an hour pitches
Credit to: supermario9000

Programmers Screen - At the title screen, hold A+B and press Start to view the names of the game's programmers.
Credit to: Ryan Rider

Credits (Japanese Version) - Pick 1 Player Mode, select the "N Team" and enter as the password "1198". Beat all the teams and at the ending, when the player is getting thrown up and down in the air, hold Start to go to the title screen. Once on the title screen, wait 5 seconds and the credits will appear.
Credit to: ReyVGM

Inside the park Homer-bunt - This trick only works in 1P mode, against the computer. Use a left-handed batter and bunt. Try to get the ball to hit the right side of the bat (close to the batter). If you do this just right the ball will roll slowly past all the computer's outfielders (and infielders) and by the time they catch up to it, you'll be at home plate.
Credit to: sharkxvd