If one is using a drop away rest, what holds the arrow in place prior to drawing the bow? For example,on short and final approach an arrow is knocked for sure, what keeps if from going all over the place?

Usually, you will build up a trough or use one that may be provided with the rest, Be careful though with some of the after market holders. I have seen them pull loose too fastand flip the arrow off, almost like the same symptom as nock pinch.