Drawing a weapon as they entered would have been premature.
Waiting until they began beating me would have been too late. This seems like a no-win situation.
Unless you consider the the third option--- which would be drawing your weapon in between the first two. Drawing a weapon when a violent attack looks imminent sounds like a good tactic to me. Imminent would include other people being assaulted.
Don't know the specifics on that train, but I remember a fellow named Reginald Denny who surrendered like a meek little lamb and suffered brain damage to the extent that he "just doesn't have any animosity" toward those who crushed his skull and laughed about it while blood poured out of his head.
Denny wasn't armed, but even among folks who carry, there seems to be those looking for a way to justify surrendering. Then there are those looking for a way to fight back
Don't know how things are layed out on the transportation system, but BASIC alertness and planning taught to those who carry would put you at one end or the other so you don't end up between two groups of thugs.
I'd rather envision a bunch of punks coming toward me down a narrow aisle thru gun fire slowed by having to step over the bodies of their friends fast piling up on the floor.
Been more than one mob of thugs back off after a couple of 'em hit the deck. They might even hurt each other fighting to be the first out the door when the train stopped.
NO, I don't know that it would happen that way, but that's a better scenario to envision than looking for a way to give up and surrender. Isn't it? It's called mindset
Just my thoughts on the matter.