The plaintiff has the burden of proof. Any negligence or complaint against the doctor needs to be upheld. The doctor needs merely to represent and defend himself which is what they're unions and legal teams are for. Nothing happens without an accusation unless an internal investigation is the catalyst.
The plaintiff has the burden of proof. Typically, in fact, the plaintiff must find two doctors which agree with his contention before he can even file a case. Then the plaintiff will be allowed to go forward.
The Plaintiff carries the burden to prove the doctor deviated from acceptable medical standards of case found in the local community, before a jury can conclude medical malpractice occured.
It is more complicated. The plaintiff does have the burden to prove the case by a prepoderance of the evidence, meaning 51%. But there are also legal assumptions of proof.