You can force the opposition to miss by holding down fire while a
player takes a shot.  The ball will be blocked, knocked over the net,
or saved by your goal keeper.

You can prevent the opposition scoring from a penalty shot by
pressing 'P' to pause the game immediately after an opposing player
kicks the ball.  Hold the joystick in the same direction that the
ball is travelling.  Unpause the game to save the goal.