What is an unrestricted production?
A single rule can not be "unrestricted".

The whole set of rules is $(T \cup N)^+ \to (T \cup N)^*$. So the class of unrestricted grammars may use any rule from this set.

Restricted classes of grammars are only allowed to use a strict subset of all rles, e.g.


right-regular grammars are restricted to $N \to T^*N^{\{0,1\}}$, and
context-free grammars to $N \to (T \cup N)^*$.


By going through the Chomsky hierarchy, you will note that the rule

$\qquad zA \to xy$

is not admitted in any but the type-0 grammars; try to see why it's not a "context-sensitive rule". That does not mean it is only ever allowed in the unrestricted class -- just that it's not in any on this list. There are many more classes.