Self-defense is an affirmative protection, so the defendant has the burden of manufacturing proof: He should placed on some proof from which a jury can discover self-defense. However then the burden of proof returns to the prosecution, which should disprove self-defense past an affordable doubt.
It was not all the time thus. The English widespread legislation rule on the time of the Framing was that the defendant should show self-defense by a preponderance of the proof, and the Supreme Courtroom has held (Martin v. Ohio (1987)) that putting this burden on the accused could be constitutional. However even by then, “all however two of the States, Ohio and South Carolina, ha[d] deserted the common-law rule,” they usually have since modified their rule by statute. (The one exception I do know of is the view of some Louisiana appellate courts in non-homicide circumstances (see State v. Satterfield (La. Ct. App. 2021)), which nonetheless require the defendant to show self-defense by a preponderance of the proof; Louisiana follows the unanimous beyond-a-reasonable-doubt rule as to self-defense in murder circumstances.)
In fact this does not get rid of what the rule should be. One mind-set about that coverage query is that the almost unanimous rule takes the view, “Higher that 10 responsible killers go free than one one who killed in correct self-defense go to jail for a very long time (or be executed).” The Ohio rule, which can be the historic Framing-era rule is, “It is barely worse for one responsible killer to go free than for one one who killed in correct self-defense to go to jail for a very long time (or be executed).” And naturally one can take into account variations of those guidelines as one shifts the burden of proof, or units a quantum of proof at another place, corresponding to clear and convincing proof. However the present legislation is fairly clear,