It looks like the defendant is not constrained to the limited defenses of 'duress,' and 'self-defense' which always seem to refer to imminent BODILY injury, rather than a threat to liberty. But the Ohio Constitution says that we have the right to defend our liberty, so I should be able to use force/threat to defend against threats to liberty (e.g., kidnapping).
Looking at some case law precedents, it seems Ohio has a definition of affirmative defense as ANY 'justification or excuse' --
In a description of the case below, note they make a up a non-conventional defense of 'blackout' which they say meets the definition of an affirmative defense since it justifies or excuses the conduct --
"Writing the Court’s lead opinion, Justice Patrick F. Fischer stated that under Ohio law, the defense of a blackout meets the definition of an “affirmative defense” in R.C. 2901.05(D)(1)(b). Justice Fischer also concluded that requiring Ireland to prove the blackout defense by a preponderance of the evidence did not violate Ireland’s constitutional rights. "http://www.courtnewsohio.gov/cases/2...p#.W_tqhehKjIU
And the Text of R.C. 2901.05(D)(1)(b) --
"(D) As used in this section:
(1) An "affirmative defense" is either of the following:
(a) A defense expressly designated as affirmative;
(b) A defense involving an excuse or justification peculiarly within the knowledge of the accused, on which the accused can fairly be required to adduce supporting evidence."