All I'm saying is that the thing we refer to as railroading....the feeling of having no choice as a player....can be caused by another player.
Except..."railroading" as the term is usually used is not about
feeling like you have no choice.
It's about
literally not having choices. About any time you
attempt to make a choice, within the game (as opposed to the out-of-game choice to leave, which
I certainly hope is always present), someone makes it so that choice either is nonexistent, or doesn't actually produce different results.
And a player cannot do that latter thing. A player is not capable of saying, "Oh, you want to go to the docks? Well...um...the docks are being repaired! A ship came off the moorings and caused damage, so the docks won't be accessible for several days." D&D, and games like D&D, only give players such power in controlled bursts, if they give it at all. (I, personally,
like giving my players that power, but that's because I trust them to use it wisely.)
A player can bully other players, but bullying isn't part of "railroading," even though it ends up in a similar place. A player may interrupt or jump in front, thus preventing other players from getting the chance to participate in the first place, but again, "railroading" does not mean "not being allowed to participate in the game or decision-making" any more than it means "feeling like you have no choice as a player." Railroading means there just
aren't choices.
You very easily could have a heavily railroaded game where no player, ever,
feels like they have no choices, because the DM knows the players well (or is incredibly good at predicting them, or really,
really lucky). All that even though they were always on a railroad track from point A all the way to point Z, stopping at every letter on the way, in alphabetical order. Doesn't mean it's any less "railroaded" than the game where the players get fed up and leave due to constantly having their off-rail choices nixed. One might even argue it's
more so, because the train never gets derailed.
Similarly, you could have a game that
truly is wide-open, but players could
feel like they have no choices. As an example, I have a player who is very shy about roleplaying. He doesn't want to roleplay "wrong." Even though we all know, there really isn't a "wrong" way per se--there's certainly
impolite things you can do, but he's a perfectly polite player (albeit cracking a lot of jokes) so that's not a concern as far as I can tell. If you had a game full of players like him, worried they were going to "play wrong," they could easily
feel like they have no choices at all, despite the DM actively avoiding railroading as much as humanly possible.
Other players could as well. Often you see this when one player wants to talk to NPCs and another initiates a combat .
Is that actually a loss of
agency though? Like...yes, it's a conflict between players, but if the DM is running things competently, such actions should not automatically win consistently in one direction or another. If the problem is happening
a lot, the group needs to sit down and have a talk about what things the players want from the game and whether they're actually enjoying the stuff on offer. (This has been a problem for me; I started off running mostly combat and minimal intrigue, and then it flipped to mostly intrigue and minimal combat, so I'm trying to balance out the two things.)
Yes, two players can butt heads, and when that happens, you need to use some kind of resolution method to fix it...but if that truly meant a removal of agency, then
all games ever played have been railroads, because you get
exactly the same problem with something like "I want to attack the bad guy" and the DM saying "roll to attack...oh, sorry, that doesn't hit its AC." That is
literally exactly as "agency" removing as
P1: "I want to negotiate with the NPC."
P2: "No! We have to attack NOW!"
P1: "Absolutely not, these aren't bad guys, we just need to talk to them!"
DM: "Not budging P2? Alright. P1, give me a Diplomacy roll, P2, gimme Intimidate. Whoever rolls higher wins. If it's a tie, whoever has the higher total skill bonus wins. [roll] Oh, sorry P2, P1 beat you by three points, looks like we're negotiating this one. Don't worry, there'll be fights later, I promise."