Why do people tap the back of cameras during filming?

Question

https://www.youtube.com/watch?v=bYWAHuFbLoc&t=58m49sAt 58 min 49s, the video above shows on-set footage of a film crew. (Link is setup to start playing from there.)For a few seconds, it shows people following the camera and repeatedly tapping the back of the camera.Why are they doing this? Is this still a thing with modern equipment?

Answer 1

I believe the man in all of those clips was JJ Abrams. He explains in a behind-the-scenes video for one of his Star Trek movies that he does this to get a genuine shakiness to the footage instead of having a machine shake the camera or add a shaking effect in post.