In the next session that I am planning, the players are being chased around by an assassin. After they are ambushed, they will end up having to try to lose their attacker by navigating around the pedways and alleys. What skill would this be? Astrogation could work (navigation), but that seems to be more for starships. Since they are familiar with this planet, would they use Knowledge-Outer Rim? The planet is almost entirely criminal (think Nar Shaddaa) so would they use Knowledge-Underworld might make more sense than Outer Rim. Because of the crowds, coordination would also be logical.

In addition, they would probably roll it as an opposed check, against the assassin chasing them. But what would he roll? All of the above could be applicable, but also perception, as he is trying to chase them.

Streetwise.

2 hours ago, Blackbird888 said:

Streetwise.

This, unless it's a foot-chase, where you'd use athletics (like once the assassin spots them and they take off running; piloting if they're driving something). However, I'd probably allow Underworld, Outer Rim, and other checks to help generate other advantages during the chase, or perhaps specific places where you'd use them - i.e. use an Underworld check to identify where one gang's territory ends, in the hopes of using a checkpoint of some sort somehow.

3 hours ago, Yaccarus said:

In the next session that I am planning, the players are being chased around by an assassin. After they are ambushed, they will end up having to try to lose their attacker by navigating around the pedways and alleys. What skill would this be? Astrogation could work (navigation), but that seems to be more for starships. Since they are familiar with this planet, would they use Knowledge-Outer Rim? The planet is almost entirely criminal (think Nar Shaddaa) so would they use Knowledge-Underworld might make more sense than Outer Rim. Because of the crowds, coordination would also be logical.

In addition, they would probably roll it as an opposed check, against the assassin chasing them. But what would he roll? All of the above could be applicable, but also perception, as he is trying to chase them.

Stealth.

Navigation uses Streetwise in Urban environments or Survival in the wild.

17 hours ago, Yaccarus said:

In the next session that I am planning, the players are being chased around by an assassin. After they are ambushed, they will end up having to try to lose their attacker by navigating around the pedways and alleys. What skill would this be? Astrogation could work (navigation), but that seems to be more for starships. Since they are familiar with this planet, would they use Knowledge-Outer Rim? The planet is almost entirely criminal (think Nar Shaddaa) so would they use Knowledge-Underworld might make more sense than Outer Rim. Because of the crowds, coordination would also be logical.

You're probably going to need to anticipate (or wait and see) what different tactics your players might adopt and adapt accordingly. I'd probably prepare a few options if this is a key encounter.

If they are just running blindly then the normal chase rules apply and you would usually use Athletics as a competative check or if there are obstacles in the way, you might want to use Coordination where appropriate.

However, your players might want to take a different approach, such as, as the pirate indicates: trying to hide using Stealth.

17 hours ago, Yaccarus said:

In addition, they would probably roll it as an opposed check, against the assassin chasing them. But what would he roll? All of the above could be applicable, but also perception, as he is trying to chase them.

On the type of check, there are opposed checks and competative checks. The choice probably depends on the situation, though I do feel there is some overlap. Typically a chase is about competative checks as the two parties attempt to see who deals with a 3rd party obstacle better and so closes or widens the gap accordingly.

A competative check has both participants roll their respective skill Checks against the difficulty of the challenge and the most successful is the winner, just like with Initiative but utilising an actual difficulty.

For navigation (Say they're not running but instead trying to out-navigate their pursuit) I would use a competative check with Streetwise (or Survival if in the wild).

If your players opt to hide from the assassin, then this is likely to be an opposed check: Player Stealth against, presumably, Assassin's Perception.

An opposed check would take the Assassin's characteritic & Skill and make the difficulty for the players out of that.

Edit: You might also consider supplementing the chase with additional checks for boosts, setback or narrative direction. Here you might have them roll Streetwise to avoid getting lost, or Leadership to incite a crowd to block the assassin.

16 hours ago, Blackbird888 said:

Streetwise.

Seconded. (If you were performing a similar encounter in a non-urban environment, you would use Survival ).