IMO this is a perfectly reasonable question, amenable to a common law analysis: (1) indicates that A has committed the tort of false imprisonment (Restatement of Torts, 2d, §35). Because of 2-4, we can see that A intends to confine B (though vide infra). The confinement is complete (§36), this being a single aisle plane although the same would be true if this was a 5-aisle plane. A has no authority to confine B (§ 41) and is not otherwise privileged, and is accomplished with a physical barrier (§38). B knows that he has been confined (§42). B is "privileged to use any means of self-defense to protect himself against confinement which he is privileged to use to protect himself against a harmful or offensive contact or other bodily harm" (§68). B uses reasonable and minimal force not likely or intended to cause death or serious bodily harm (§63), force which is privileged and thus protects B from being subject to liability (§10).
A commits the tort of battery (and a second round of false imprisonment) by taking B down (§13). A is not privileged to use force in self-defense. There is no reasonable belief that B will spontaneously turn on A and use further, unprivileged force – A is simply punishing B for his minimal use of force in self defense, so A's final act is not privileged.
There is a related but distinct scenario that adds a material fact, which could change the analysis: C calls out "Excuse me, my flight flight leaves in 15 minutes, may I pass?" whereby A allows C to step ahead of him in the queue. A has no obligation to let anyone jump the queue, but may consent to inconsequential contact which might constitute battery. It is reasonable to conclude that there is apparent consent (§50) given to anyone (§52) when A makes way ("making way" is a publicly-available fact, but "for C to pass" is a private fact of A's state of mind which B cannot reasonably infer: except, B has heard the "May I pass?" request). So the analysis really hinges on how to interpret 2 and 4. Coupled with 6, we (jurors) have a preponderance of evidence showing that A intended to confine B, and battered him when his confinement failed.