Originally Posted by Brad Gerbrandt
When I worked as a strength and conditioning coach I had almost all my athletes learn the regular kip. It's already be mentioned, but think of the a volleyball player about to spike a ball...it's pretty much exactly the same position as the forward position of the kip. Many other skills have a similar position, throwing a ball, serving in tennis, kicking a soccer ball...
There are plenty of movements that teach you to forcefully open your hips, but only a few that teach you to forcefully close them. The regular kip does a good job of that.
However, I love the butterfly kip. In Crossfit workouts, unless there is chest to bar, I always butterfly now. It's fun and fast. I haven't noticed either one to be harder or easier on my shoulder as long as you don't drop straight down in the butterfly.
^^ Right on...
Going between the arch and hollow of the beat swing (regular kip) is fundamental, you don't have to practice it with a pull-up, but it should be practiced (unless of course previous injury dictates otherwise on your shoulders).