Wii Sports

1.learn how to spell the word WII
2.go look at the cheat section for this game
3.scroll down the page until you find your answer

quote from the cheats page:
"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.
Contributed By: Mingy Jongo."

Do you mean how to unlock the minigame or get the strike in the 91 pins?

Id rather do it manual than cheat. Move ur character to the right/left end of the lane. then aim the ball at the very first pin. dont make the aim too accurate, just make it a bit "off the spot". Or you could just cheat =(