Put Amir Khan and Achmed Khan on the same team and both of their skills will increase. The same happens when Ashley Webber and Sidney Webber are on the same team.
Major league players will have increased skills when playing for their real life team. For example, Randy Johnson will perform better when playing as an Arizona Diamondback.
If the other team throws the ball to home play and you are on first base, you can run to second and they will not see you.
To unlock Abner Dubbleplay as a playable character, get every single certificate in the game.
To unlock Aquadome, Hit a Home Run into the water on these three fields: Frazier Field, Gator Flats and Steele Stadium.
To unlock Humongous Memorial Stadium, Get to the World Series.