If a black rider comes down kuz of a failed hide test, engages and makes an immediate attack, is there any window in there to ready a hobbit via fast hitch? I am assuming not.

Hum... enemy attacking outside the combat phase are supposed to go throught the standard enemy attack step of the combat phase. So there is one if you consider you choose the enemy as attacker, there is an action window as per the rule...

Yes, sure. In the last faq it is written: action window is open

Thanks all! Found it in the errata too!

where you find in errata ?