Unless your strikes have no power, when you hit a person, they will move. Unless they believe your strike has no power or will not land, if people see you trying to hit them, they will move.
This is not rocket science.
Depending on class size, ability, and supervision, an instructor might not want students engaging in a drill where a combination rather than a single attack or response is used. In such instances a lack of natural movement is understandable. A frozen position can enable the instructor to see the basic mechanics of an attack to ensure that it has been delivered correctly. However, if following their attack, a training partner remains immobile to receive a combination of responses, their body position and combination employed itself becomes incredibly false.
There is another way.
If an instructor wants to see whether a student has the correct mechanics to deliver an effective technique, and wants the student to gain such mechanics, they can have the student strike impact equipment. It is the tried and tested method to develop and assess ability used in many martial arts. If an instructor wants a student to learn how to spot the telegraphs of techniques and not get frightened by them coming towards them (a potential benefit of the static position training form of basic sparring), then they can have them hold pads and receive and observe the technique. This is once again an effective method used in many martial arts.
But what if we want to train combinations? What if we want to train combinations that combine trapping, holding, unbalancing, grappling or throwing alongside strikes made by any part of the body to any part of the body?
Whether you hit or miss a person, the natural response is movement. Effective combinations create and exploit the predictable response of that movement. Effective training therefore means that the more participants are allowed to move naturally, the faster they will develop the ability to read, anticipate and create movement that achieves their aims, whatever the anticipated arena. That natural movement not only includes the freedom to evade or counter, but also crucially the need to move the body on pulled or simulated contact to give accurate positions for follow through redundancy techniques or recovering the initiative to counter-attack. That reactive movement is fake as no injury has occurred (although impact has), but it is arguably less fake than staying still and holding a position as if no strike had happened.
Reactive Position Training (RPT) works effectively with the type of close quarter combined grappling and striking training I teach, but there is no reason why it cannot effectively be employed by anyone in any basic ‘one-step’ kumite with pulled-impact strikes going through targets (as opposed to fast thin air strikes stopping in front of the target) so long as practitioners are afforded other opportunities to perform their techniques full power. Before I switched to integrated kumite drills that allow progressive free play through options right from the initial grades, the introduction of RPT in single step drills to build an understanding of predictable response and appropriate redundancies was the first major change I made to how I drilled in my clubs. Such training at an early stage builds a natural understanding of correct distancing and of the implications and limitations of techniques and combinations. RPT also forces both partners in two man drills to always be actively moving and engaged even at the most basic level of training, and that creates the appropriate physical and mental attributes for dynamic and alive drilling.
Many martial arts devote a lot of training time to fake attacks where no-one hits each other. It’s a compromise that delivers safe paired training, improves reaction time, and works movement. Reactive Position Training (RPT) however is an alternative compromise that enables students to make safe ‘fake’ contact through reactive targets with realistic post contact positioning in conjunction with developing safe true unrestricted power delivery on impact equipment. While speed is slowed on impact, speed of attack or defence does not have to be compromised and can increase with proficiency as with any martial arts training. Pulling the force of a technique prior to pushing it through a person is simply a variation on the common training format of stopping a technique artificially in thin air rather than allowing impact to stop it: both pull contact, but the different ways they do so have implications for power development, posture, distancing, joint health and follow-through positioning and techniques.
Your training determines your results. If you don’t already practise it, I advise giving RPT a trial. It may not be easy to make the switch from ingrained habits, but when you do you may wonder why you’d ever do anything else.