Breaches of the Standard Of Care
A "C" is adequate from the point of view of professional competence.
Basically true. The attorney has to do an adequate job, not an excellent one.
Some conduct that is unethical under the Rule of Professional Conduct that apply to your attorney (e.g. an attorney's ethical duty of competence and diligence) are breaches of the "standard of care" and if your attorney breaches the standard of care by (1) failing to act with the care of a reasonable attorney under the circumstances (2) as established by expert testimony in most cases, and (3) this causes an inferior outcome then (4) you are entitled to damages equal to the difference in economic value between the outcome that resulted from the negligence of your attorney and that outcome that a reasonable attorney who adhered to the standard of care would have been able to secure. (The existence of an attorney-client relationship is another element that must be established, although in the heartland of attorney malpractice cases this is often undisputed.)
Normally, this requires proof of a "case within a case" once you have met the threshold of showing a breach of the standard of care, to show how a reasonable attorney would have secured a better outcome on the merits.
Sometimes non-economic damages (i.e. pain and suffering) can be awarded in specialized circumstances, for example, when the negligence causes you to be incarcerated or civilly committed or to receive inappropriate medical care.
But the lawyer must not earn an unreasonably bad result, that is, an
This is not correct. The result can be horribly awfully bad and still not give rise to attorney malpractice liability. If the conduct of the lawyer in representing you is an "F" and that causes a bad result, then there can be liability. But, if your lawyer acts with the care of a reasonable lawyer, and a judge or jury just doesn't see the case your way and you get a horrible result, that is not actionable.
Breaches of Fiduciary Duties Other Than The Standard Of Care
Some conduct violates other ethical duties of an attorney which involve facts that are separate and distinct from the conduct that fell beneath the standard of care, most often implicating the lawyer's duties of loyalty, confidentiality, or candor to a client. If the same conduct and facts implicate both the standard of care and other fiduciary duties, usually, it will be treated as a pure breach of the standard of care case.
Most, but not all, states in the U.S. recognize a separate and distinct cause of action for breaches of these duties which overlap with an attorneys' ethical obligations.
But, a breach of a rule of professional conduct does not in and of itself give rise to a private right of the individual aggrieved to sue the attorney who acted unethically. Instead, a breach of a rule of professional conduct merely authorizes sanctions imposed by state or bar association regulators (depending upon how law licensing is structured in a state) such as admonitions for bad conduct, suspensions of licenses, and revocations of a lawyer's license.
To give a simple example of a breach of fiduciary duty that is usually separate from a breach of a standard of care, if your lawyer's law firm has lawyers representing both sides in a contested arbitration proceeding, then the law firm and the lawyers involved have violated their duty of loyalty to you because they had a conflict of interest. This is so even if the lawyers on each side otherwise performed their duties for each client in a manner that lived up to the standard of care for reasonable attorneys who are not conflicted under the circumstances.
There is not a clear majority rule concerning whether breaches of fiduciary duties in a manner separate and distinct from a breach of an attorneys' standard of care requires expert testimony to establish.
Most, but not all, states authorize an additional remedy of forfeiture of all fees paid or owed to your lawyer during a time period during when a breach of the duty of loyalty existed, whether or not any other economic money damages can be established.
Sometimes non-economic damages are available for breaches of other fiduciary duties (e.g. the disclosure of highly embarrassing personal information about a client that humiliates a client in breach of an attorneys' duty of confidentiality, or having sex with a vulnerable client), even when beaches of standards of care by the attorney in the case would not otherwise give rise to a right to that kind of damages.
In an extreme case, an intentional, or even a willful and wanton, breach of professional ethics which also constitutes a breach of a duty of loyalty, for example, taking money from a client's trust account without justification for the personal benefit of the lawyer, may also give rise to a claim for punitive, exemplary, or statutory damages that are not compensatory in nature and usually are an amount up to a doubling or tripling of the amount of actual economic harm caused by the attorney to the client.
Not All Ethical Violations By Lawyers Are Actionable
On the other hand, there are many kinds of violations of an attorneys' professional ethics that are not actionable in a private lawsuit.
For example, it is generally a violation of the rules of professional conduct to be found guilty of driving while under the influence. But, even if the attorney drives while under the influence, is arrested, is convicted, and serves some non-incarceration or work release sentence as a result, while representing you as your attorney, you can't sue the attorney for that unless it gives rise to an specific breach of the standard of care for a reasonable attorney in how you are represented in your case and that causes you economic harm.
This would be true even if the attorney didn't disclose to you that he was an alcoholic, and even if his alcohol problem caused you to lose faith in his representation but the court did not allow him to withdraw as your counsel in a lawsuit (which courts are allowed to do in many circumstances).
Claims By Third-Parties
Generally speaking, malpractice cases, either for breach of the standard of care or for breach of other fiduciary duties arise from a fiduciary relationship between an attorney and the attorneys' client that exists for the sole benefit of the client. Absent some narrow exceptions, no one other than the client can bring a lawsuit to enforce a breach of these duties.
For example, generally speaking, an opposing party in a case cannot sue your attorney for professional malpractice, either due to a breach of the standard of care, or due to a breach of some other distinct fiduciary duty owed by an attorney to a client.
For what it is worth, I am an attorney in private practice, primarily in Colorado, who frequently represents clients in attorney malpractice cases in my private practice of law. The legal authorities you have to sift through to digest the law to get to the bottom line above, are quite voluminous. Also, this is an area of law mostly governed by common law case law, rather than by statutes. It would be easier to cite chapter and verse of legal authorities for more specific questions, but is rather challenging to do so without much more time preparing an answer to provide this broad lay of the land at a "forest level" of this area of law without writing a full fledged legal treatise or law review article.