To the best of my knowledge, Leap always goes first, and the waiting model standing fast may then swing. If however, the model is braced, it goes before the leaping model. I know some of this is in the FAQ that's pinned, but I can't remember if everything was spelled out. Let's both consult that, and see how this works.
To answer one part of your question, yes, Leap will take away the Ramming models, or Tusk Attack models, ability to do its' thing on the charge, because it can't charge in this situation. Great special ability.