i checked to see if this was already posted and it came up with nothing so here are all the wii sport secrets i know !
Change bowling ball color
As The screen is fading to black for bowling, hold down the control pad until it fades to bowling for these colors:
Control Pad Up Blue Ball
Control Pad Right Gold Ball
Control Pad Down Green Ball
Control Pad Left Red Ball
Change the tennis court
To change the tennis court to the blue practice court, press and hold (2) at the warning screen that shows after selecting characters.
Play Golf without maps or meters
To disable the power meter, map, and the wind speed indicator, press and hold (2), then make a selection at the "Select a Course" screen.
Silver Boxing Gloves
After you've beaten the Grand Champion, Matt, in a boxing match you'll be able to wear silver boxing gloves. To do so, hold (1) when the screen becomes black before a boxing match
Special Bowling Ball
Get to pro level to unlock a bowling ball with diamond designs on it.
Amuse Crowd in Bowling
To make the crowd laugh in bowling, move to either of the gutters in your lane, turn into opposite lane, and bowl so the ball goes over the barier between the lanes. The ball will go into the gutter in the opposite lane and the crowd will laugh.
Scare Crowd in Bowling
To scare the crowd while bowling, start the regular motion for bowling and let go on the backswing. The ball will fly backwards and the crowd will scream and jump.
91 Pin Strike in Power Bowling Training
To get an automatic 91 pin strike in the last round of Power Bowling, Throw the ball on the right or left rail (depending on if you are right or left handed) so that it stays on it the whole time. If it reaches the end without falling off, you will hear a "click" and an explosion. Then all the pins will fall down from the shockwave. NOTE: This only works on the last round.
Hope that helps !