Kinect Sports
70 Achievements
1,500
80-100h
Invasion Thwarted
Knocked down 50 pins or more in 4 seconds in the Pinvaders Bowling mini-game
30
How to unlock the Invasion Thwarted achievement in Kinect Sports - Definitive Guide
I personally found that the best time to bowl is when the pins start to reach the guide markers on the lane. It took a few attempts to get the timing right, too soon and you don't get enough pins but too late and they rush forward and it's game over.
This will likely take a few tries to get right, but it's actually pretty easy to get when you've got a good technique going on. As mentioned in "Pew Pew Pew" the pins will be on a conveyor belt coming towards you. The idea here is listen to the music which will indicate when the pins are going to speed up, like the alien ships in Space Invaders. The idea is to wait and time it, so that you unleash both balls at the same time. Aim for one side, rather than straight down the middle, as this should and if done correctly, only leave one line of pins rather than two either side. If you've timed it right, you should get your 50+ pins in under 4 seconds and the remaining pins will then reach the boundary that ends the game, so be warned.