I'll take a shot at how I would handle these. This is, of course, based on my own rules interpretation, so may be wrong. In all cases, I'm going to assume that Rossyl does not have any weapon but the bow.
a) He is pulling his bow at some men-at-arms (with only melee weapons) charging at him from 50 yards, across the bridge. They are but seconds away. How many arrows will land true before they arrive?
Hold Steady to do anything when being charged at by men-at-arms. (a miss doesn't mean you run, it just means you flinch, and the MC can have that mean something worse). After that, Go Into Battle, Rossyl does 4-harm, men-at-arms do 0. If they make it to Rossyl, another Go Into Battle, Rossyl does maybe 1 harm for his fists, men-at-arms do 4 with their swords.
b) He is pulling his bow at some men-at-arms trying to kill him, but they are crossing a ford from the other side, that will probably take a few minutes from them to cross to this side.
Go Into Battle, Rossyl does 4-harm, men-at-arms do 0. If they make it to Rossyl, another Go Into Battle, Rossyl 1, men-at-arms 4.
c) He is pulling his bow at a some men-at-arms coming to arrest him, but our hero can shoot safely from a tall tower window, which iron locked door is not readily accessible to his foes. They have a choice to try to force the entrance, which can take a long time, or run to the forest cover, which is half a mile away. It was a trap!
I would just have him do his harm. In AW, I might have him Go Aggro. Vincent says this is Go Into Battle, so probably Go Into Battle, Rossyll 4, men-at-arms 0.
If the men-at-arms were unaware of Rosyll, I would definitely have him just do harm. Murder isn't battle.
d) he is pulling his bow against a few men-at-arms which are already engaging him in melee. Our friend's Rossyll´s Fate isn't looking all that bright. I hope he still have more to do before he dies.
In my game, he wouldn't be able to use a bow like that, so Go Into Battle, Rossyl 1, Men-at-Arms 4 . In a game inspired by Legolas in the Lord of the Rings movies, Rossyl 4, Men-at-Arms 4.
In all of these, subtract armor from harm.