How is movement determined?

[Lazy_Perfectionist]

Mostly correct, thejeff. He owns everything in the province except the fortress, lab, and temple.

My experience lines up with theJeffs. Though...
IME - Assassinations happen before movement.

I'm not certain what happens when the defending army trys to break siege and the attacking army tries to pull back to friendly territory. My guess is the siege breakers attack before movement since they're already there.

What happens when a scout belonging to player Y attacks the province A belonging to player Z he's in and the defending army belonging to player Z moves from province B to Province A?

[thejeff]

Assassinations do happen first. Catching sneaking troops happen after other battles.

Siege breaking happens along with movement, since reinforcements for either side can arrive before the battle. The besieger pulling out to friendly territory happens first. Invading a different province should work normally.

I'd assume stealthy units attacking don't interfere with movement. In your example the defending army would move first, since it's friendly movement, then the scout would attack. I've seen this happen, using scouts to take 0PD provinces from the AI.