Putting it all together
The dynamic pull-up (aka kipping pull-up) involves a well-timed handoff of motion between lower- and upper-body components. The lower body starts this movement with a forward and back swing, and then hands off the momentum to the upper body.
Teaching the hip-swing portion of the kipping pull-up can be aided by having the athlete hang from the pull-up bar while the trainer initiates the swing forward and back with a forward push on the sacrum and backward push on the belly. This is one way to get a feel for the rhythm and timing of the swing that sets off the movement.