Harder throws: 

While playing defense, press A and the direction
of the base you want to throw to immediately 
before the CPU catches the ball.


Better defense:

Place the game on a harder difficulty setting for
a better defense. However, the opposing team will
be more difficult to defeat.


Fireworks: 

Hit a homerun with the home team in their stadium
during a night game.


Running:

When your running to a base tap a reaptaly to run
faster.