Rule Definition
Casting from a derived class to a base class is implicit. If you explicitly write a cast, it will work too, but it will also work in a situation where it should not, for instance if the class hierarchy has changed. Relying on implicit casting is therefore both simpler to use and safer.

Remediation
Following the example, if A and B were not related in any way, line 1 would still compile (and be equivalent to reinterpret_cast), but would be wrong, see rule "Never perform C-style cast between incompatible Class pointers" (id 8002). If A and B were related, but B not be derived from A, line 1 and 2 would still compile, but would be wrong. See rule "A pointer to a base Class shall only be cast to a pointer to a derived Class by means of 'dynamic_cast'" (id 8060).

Violation Code Sample

class A
{
};

class B : public A
{
};

A* p1 = (A*)(new B()); // 1: Violation
A* p1 = static_cast<A*>(new B()); // 2: Violation
A* p1 = new B(); // 3: OK