I don't know if I would try to shout down a nazi in an enclosed space by myself, either.

I've approached the person being verbally attacked, asked them if they're all right, showed that they're not alone. I've only done it twice, the person was being sexually harassed in both instances, but I think it's just as useful for verbal attacks of racism, as well as homophobic and transphobia. This https://itstopswithme.humanrights.gov.au/respond-racism page briefly talks about doing things like that. It also mentions assessing the situation before you say something and not "putting yourself at risk" of injury. I think someone threatening physical violence would count as a risky situation. Responding in non-confrontational ways that are less likely to result in escalation that (further) endanger the victim and yourself. It basically suggest engaging with the victim instead of the piece of shit attacking them. I think that's really useful advice and something people should talk about more. Because realistically, not everyone is suited for conformation, confrontation isn't always right answer in these situations either, and there are other options besides confrontation or being a bystander. If we project that there are not other options, I think it just further promotes complete passivity among people who are not prepared to or suited for shouting down a nazi.

Wie viele von denen die als Nazis gelten sind wohl so drauf wie unser Freund? Jemand der seinen Konflikt mit der geistigen Behinderung unbehandelt auf der Bühne des Lebens spielt? Dass Neo-Nazis der Kritik würdig sind und ihre Ideen keinen Halt finden dürfen in unserer Kultur ist klar. Von der rigorosen Reinhaltung des deutschen Geschlechts, der Ausgrenzung Anderer, dem Wahn den Feind im Fremden zu erkennen und ihn nur dann temporär zu akzeptieren, wäre er oder sie aus dem gleichen Holz geschnitzt, jemand mit sehr begrenzter Liebe. Aber ein Solcher ist noch kein "Ich töte deine Kinder"-Nazi. Mit den Gemäßigten müssen wir in einen Dialog treten, respektvoll, ich habe es gemacht und hoch interessante Dinge festgestellt. So ein Gestörter gehört allerdings Behandelt und weg von der Gesellschaft. Hättest du mehr Zeit gehabt könntest du dir eine Strategie überlegen. Vielleicht dich mit anderen Passagieren zusammentun und ihn gewaltfrei (falls möglich) dingfest machen aber in so einer Situation kann man das nicht verlangen.

The goal to be a fighter needs preparation, the will to hurt or kill and the ability to cope with the results. It is not determined by physical superiority, real or observed. Even a 52 kg girl like me could bring down a man of double the weight, but the attack has to be skilled, trained,sudden and effective driven by a will with no doubt. Almost nobody shares these. We civilised people are full of doubt, untrained, unskilled and most of all, we totally lack the will to destroy. And the enemies know this. Our bodies are traitors and we show all the signs of lacking the will and skill for a fight, so it is easy to calm us down. But as a group we should be vocal about wrongdoing. Sad enough we share with any flock of animals the lack of solidarity. We hope the aggressor will just attack another zebra and eat it and leave us. And that is what happens.

I would say that there's no objective right or wrong and it's up to you to decide whether what you did/didn't do was right or wrong, but then, I'd probably be a hypocrite if I said that because there are probably other questions where I'd answer that it's either right or wrong.

In this case it's just a matter of how much you're willing to stick your neck out, who you define yourself to be. And there's a risk/reward trade-off to consider (in this case the reward isn't for you, it's for the foreigner). I personally think it's completely fair not to say anything because the Nazi could choose to kick your ass and that's not necessarily worth comforting the foreigner, who may not be that affected by it in the long run anyway.

If the question is about standing up to the Nazi for its own sake, because the Nazi is wrong and should be yelled at, I would say there's no point in that because you're not going to change his mind. Just let him be who he wants to be. The only point in standing up to him would be for the sake of the victim.