Hello Cabdriver, what you saw them do we call "kicking" If the yard is flat or not on a grade you kick the cars to get them to roll down the lead or ladder track into the rail you want them. Here in Sparks Nevada our yard is on a 1% grade so when we switch on the top end, all we have to do is uncouple the cars. To do that we bunch the slack so the uncoupling lever can open the knuckle which is enough movement to get the cars rolling. We don't let them roll too far and the track they are going into must have cars in it already with hand brakes applied to them. When I switched in Stockton, we could switch a 100 car train in about 90 minutes, if we had a lot of single cars to let go.
Cheers,
Greg