Fleeing mount and ranged attacks

[Maelorn7]

Hello. In one of sessions where I act as a GM we had an encounter where the ranger archer PC started on a riding horse and got attacked by orcs jumping out of ambush.
The rest of the party started the close combat.
The ranger's horse immediately got frightened 4 and fleeing. I supposed ranger should've calm it down with Nature to normally act, but he actually said "I'm fine with the horse fleeing, I will just shoot from it with no spending actions for movement, thanks".
Actually this fleeing and frightened helped the ranger to avoid combat and move 3 times (with horse's actions) and shoot 3 times in a single round.
Is it intended? Or are there any rules preventing it?
I can easily correct it as a DM with houserulings (e.g. giving -5 to hit), it's just that I want to understand if there are any CRB restrictions for such situations?

[Fuzzy-Wuzzy]

Neat!

The mounted combat rules assume your mount is calm and doing what you tell it; there aren't any rules for the effects on you of riding a frightened and/or fleeing mount. So I believe what the ranger did (and didn't do) works fine by RAW, but is probably not quite intended. Giving the rider of a fleeing mount penalties sounds like a good idea to me. Maybe make them clumsy 1 or even clumsy 2.

[Adjoint]

I would say that a frightened, fleeing mount stops beeing willing to carry a rider. That would mean that normal rules for riding (which assume a willing mount) may no longer apply.

There are no specific rules for that, so some need to be made. I suggest forcing a check to stay in the saddle, something like this:

STAY IN THE SADDLE, cost 1 action, Acrobatics check
Requirements You are mounted on a mount that is is moving on its own without you Commanding it.
Critical Success You stay mounted with no penalty.
Success You manage to stay mounted but are clumsy 2.
Failure You manage to stay mounted, but you must use all your actions to keep balance. Your turn ends.
Critical Failure You fall off the horse and become prone. Your turn ends.

The DC should be set based on how violent the motion of the mount is. Staying in a saddle of a fleeing mount sems like an Expert task to me.

[Maelorn7]

Well if there are no rules for staying on the mount I suppose I will make them myself. Possibly mount will flee on their initiative and will try to "Buck" the rider.
Also staying on the mount will automatically make the rider Clumsy 2 with possibility to "Balance" if the Rider wants to stay mounted and not suffer from Clumsy.

[Fuzzy-Wuzzy]

Horses do have a Buck reaction, DC in their Bestiary entry, rules on Bestiary page 342. Technically it can't Buck against an already-mounted rider unless they try to Command it, because the trigger is Mounting or Commanding, but if you want it to Buck anyway (up to 1/round and does not eat an action!) at least there's rules for that. Note that being clumsy 2 will give a -2 to the Reflex save vs Buck.