Imagine a jump mishap throws a ship way the hell out of the Imperium or whatever bloated weapons factory empire you have set up. The characters find their ships in a small cluster of stars cut off from the mains galactic civilization. In the Traveller setting the Islands Clusters are ideal for this, colonized by STL asteroid ships and developing independently for thousands of years. Imperium? Never heard of it.
The characters find themselves the object of a witch hunt for a simple reason. Their ship has a reactionless drive. Civilization here has only developed reaction drives. A reactionless drive opens a whole can of worms which others have detailed far better than I. Near light speed projectiles are a real bummer. they make any polity effectively helpless against long range bombardment.
Okay I mentioned a bunch of double talk ways to limit the top velocity of reactionless drives, everything from ark matter build up to upsetting ghosts. Presumably there is such a limit in the characters' technology allowing their nation to flourish.
But the local won't believe this. The player characters are the scouts for an armada of world wreckers. So wherever they go, they are hounded. Some warlords want the drive for themselves. Others want to make sure the others don't get it to keep business going on as usual. What can you do? The chase is on!
The characters want to reach a point where they can return to their home stars. Perhaps there is one wormhole they need to reach. Perhaps they only need time till a burnt out whatsit is repaired. regardless they have to keep moving. Their ship has the edge in delta vee (nearly infinite call it). Of course the locals may have attack craft with higher accelerations making top velocities moot.
Then there's the issue of fuel/slash propellant. The local witch hunters can gas up at the nearest starport. Our intrepid crew will have to beg borrow or steal their fuel wherever they can. Wilderness refueling in Traveller is hard enough without being on the run. Also gas giants will be the first place the locals will look for those physics flouting invaders.
Equal and opposite reactions. It's the law.