We had this drill in baseball, if it's the same thing. It was mainly for the infielders, even though we all went through it. The coach would roll the ball on the grass and we had to stay in front of it without crossing our legs and when we bent down, we had to bend from the the knees with our opposite dominate leg forward. For me, I'm right handed so I had to step forward a little with my left foot as I bent down to pick up the ball and throw.
I can't explain it too well, but it's for hand eye coordination. For football, the thinking is most likely if you can grab this little baseball, you'll be able to grab the football. I'd disagree because the football bounces differently and you should be practicing that. By how the ball is hitting the ground you can easily predict the direction the ball will go.