What is physical?

I have encountered people who argue against defining things from a physical perspective by trying to restrict physicalism to physics.  I have seen claims that biology, psychology and so on are beyond the physical as defined by known physics.  From there, some of these people move to metaphysical beliefs such as the mind being some kind of supernatural thing separate from the brain.  But we are not talking about just physics when we talk about the physical.  Physics relates to an aspect of the study of the physical.  It does not mean that the physical can only be defined as what physics defines.  Things need to include what's known in physics but it does not end there.  The physical purely as what physics defines is a misdirection. So I thought that it may be useful to clear the air.  When I refer to the physical, I am referring to physical reality.  I could use the word realism but that is used in a lot of contexts.  Let's look at it this way.  We all have a common realm in which we can interact.  We define this as physical reality.  We can study various aspects of this reality.  I suggest that anything which begins from somewhere outside what's known in reality is less tenable.  Ultimately, things need to fit in or have a relationship to physical reality.  If something outside known reality is posited, then the idea needs to have a consistent connection, at least in the theoretical, back to known reality.  As new knowledge arises, the ideas need to be modified to fit the known.  But a lot of people believe that supernatural beliefs do not need to follow any of this.  But there is a question which I have yet to get a good answer.  "Why not?"