After many frustrating hours, I finally unlocked this today and want to give some tips:
Yes, you have to squat just about every time to pick up the basketballs as they are thrown at you. The physical motion is squatting with both hands down, then stand up, bring both hands to your chest as if you're holding a fake ball, then I raised both arms up in a tomahawk chop motion. Whether the ball goes in or not depends on 3 factors:
1) aim: move the ball so that the peak of the adidas mountain logo is under the middle of the basket; it will go in 99% of the time.
2) pace: for me, what worked was coming out of the squat, just allowing for left/right adjustment so that the aim was right, and then immediately tomahawk chopping. When I aimed for too long, it always seemed to miss.
3) speed and height of chopping motion: find a speed and height that works for you, and do it robotically, 100% of the time, every shot. You are doing the same motion over and over, like a bricklayer. You'll need to have muscle memory of the correct shot so that it's automatic and you don't hesitate too much.
I know human beings usually shoot a basketball with one hand, but the two hands worked MUCH better for me. When I shot with one hand, it was unsteady and inconsistent. Also, I found that left-handed under the options worked better, perhaps because my kinect is to my left.
Once the ordeal begins, you will see a multiplier go up on the top left. This doesn't really help you keep count after 5 shots, so don't panic when it maxes out at 5X, that's just the score multiplier. After 10 baskets, you will get a little notification in black on the bottom left of the screen for 10 in a row...only 5 to go! Then once your 15th basket falls, you will get an 'on fire' message in the middle of the screen, and then about another 10 seconds after that your cheev will pop. I had time to miss my 16th shot while swearing that the achievement was glitched, but it just takes a little time to pop.
Congrats on your new achievement! Everything else is cake for this game.