Ferris Wheel and stepover are terms that Paul Nyman (coachxj on this board) came up with to describe actions in the mechanical sequence of throwing. Both are quite complex ideas. If I understand correctly, Paul talked about ideal lower body action as rotational (creating rotation of the pelvis). He called this a "merry go round" to give a mental image. The rotation of the shoulder girdle (and the attached throwing arm), he also referred to as a merry go round type movement. The torso that connects the two, he referred to as a merry go round type motion- still rotational, but in a different plane. Pitchers who have a high release point and reach back by tilting their shoulders during their stride have a noticeable ferris wheel action. Andy Pettitte is a good example. Pitchers who maximize both the merry go round AND stepover usually have exceptional velocity. Examples are Sandy Koufax, Tim Lincecum (when he was younger and throwing 95-98), and Aroldis Chapman. The stepover refers to what happens to the stride foot of pitchers who load their hips well. It almost looks like they step OVER something just prior to footplant. This is a consequence of good pelvic loading. All of these concepts can be found on the old Setpro message board if you look enough. There is a LOT of great info there, but be prepared to think and research, because it's pretty complex stuff.