Wall Breaker!
When you are playing the Tennis 'Target Practice' game if you don't hit the target you will hit the brick wall around it making the part of the wall you hit go a slightly darker colour. When the bricks get dark enough they will create a hole in the wall and if the ball goes therough the hole the training session ends.
More tricks, tips and cheats for this game are right here - Wii Sports cheats
Comments for this cheat