I do not know for 100%...but I believe Frost went to Stanford because he was a QB and he had dreams of being in the NFL--as a QB. Bill Walsh was, at that time, the HC of Stanford and so Frost picked the school and coach he thought was best suited to get him NFL ready. Ironically, at Stanford he ended up at Safety. I think, and I am relying on memories years past, but Frost did get a shot at QB while at Stanford and it just didn't work. He was too good of an athlete to keep on the bench, so Walsh put him at safety. Anyway...that's my hazy recollection.