Roleplaying games tend to follow the rules of Hollywood movies, not physics. So a blast from some sort of gun can easily throw the target backwards a considerable distance, while the person firing the same shot feels no significant recoil at all.
In reality, a bullet carries only a small amount of momentum. The high velocity gives it a high kinetic energy, since that scales as the square of velocity, but the small mass means the momentum remains relatively tiny. So it can impart a lot of damage, but cannot really throw a person backwards significantly.
But what if you turn this on the head and make it so that weapons actually fo throw large amounts of momentum? Now you have a person wielding what is effectively a cannon. When it hits a target, the massive cannonball smashes them backwards, just like in the movies! But the cannon also has a large recoil, and throws the firer backwards the same amount.
What if your game only has ranged weapons that behave like this, for some reason?: Variant physics, they're actually more effective at taking down the intended targets, or maybe just nobody has figured out how to do them any differently. Anyone firing a weapon has to brace themselves or be knocked flat. You could easily play this for laughs - imagine some sort of Ghostbusters campaign where you need these sort of weapons to affect supernatural entities. But you could also do it in a gritty setting - say something like Judge Dredd or Warhammer 40,000.
(N.B. We don't know if this would be fun for most people. We just throw ideas out there and hope the right people see them! Hopefully somebody can have fun with this!)
Commentary by memnarch (who has not seen the movie)
Whoa, Chewie actually got hit? Thank goodness for protagonist importance so that was just an injury instead of a death like almost every other blaster shot. On the other hand, I suppose this is rather par for the course for the movie in showing how dangerous things are at the moment. If this matches up with the other arm injury though, Chewbacca will be just fine in a couple scenes, and maybe a bacta tank bath.
Also it's neat to see the continuity from Episode VI for Han/Yanni never using the plasma crossbow. That's been over a year ago at least! I would have forgotten a line like that after a few months unless I'd made a note specifically for that. Given that Ben is quite methodical and had helped keep Han's traitorous plans in motion without Han messing things up too much though, I would not be surprised if he did make a note for it. I'd also not be surprised if Yanni doesn't give the crossbow back without some persuasion.
Yanni wanting to blast the door controls? That will either go extremely well or incredibly horrible. With the hotwiring attempt working about as well as all of the other times doors were closed, I bet this is what will open the door in the end. Because blasting the door down has to work eventually, and why would the astromech droid be used for hacking or repairing anything?
Commentary by Keybounce (who has not seen the movie)
OK, a plasma crossbow sounds like "Awesome but Impractical". If you can generate a bolt of plasma, why would you bother with a crossbow form? If you had something that could fire a projectile like a crossbow, and are going to stick a plasma tip on it, why not just come up with a way to shoot off plasma without having to go through the massive strength requirement to cock the bolt?
Unless the idea is that someone else would have trouble using your weapon. Chewie's strength is such that he can prep the crossbow. Once prepped, someone like Han can fire once - only. They would not have the strength to fire it again, so Chewie would know that if his weapon was stolen, whoever took it would be limited in the damage that was done.
For game balance reasons, having that "Strength to cock" requirement would be fitting - high damage weapon with a restriction.
From a "reasonable physics" point of view, there's no good reason to make this device. Which means the only in-world reason to have this is if you expect your weapons to be stolen all the time, so as a society you develop weapons that can't be used by outsiders.
Which really seems like a strange rationale.
GM: The remaining Guavian fires. <roll>
GM: Chewie, you’re hit! <roll>
GM: 15 damage to the right arm.
Chewbacca: Ow! That’s over Lameness Threshold.
Yanni: Chewie! You okay?
Chewbacca: I’ll survive - if that Guavian doesn’t kill us. I daresay it’s time to reconsider my prohibition on you ever using my plasma crossbow.
Yanni: I grab the crossbow and fire at the Guavian! 16!
GM: <roll> The blast hurls his limp body 3 metres backwards!
Yanni: Awesome! I’ll blast the door controls!
Chewbacca: Reconsideration complete. Prohibition restored.