1893, "boy who travels with a tramp and begs for him," of unknown origin; his protector/owner was a jocker.
Online Etymology Dictionary, © 2010 Douglas Harper
Examples from the Web for prushun
It was the tenderest good-by I have ever seen between a prushun and his jocker.Tramping with Tramps
I was never a prushun, for I did not take kindly to possession.The Road
On the road the lad is called a "prushun," and his protector a "jocker."
As a rule, the prushun is freed when he is able to protect himself.
The majority of them prefer a prushun to a woman, and nothing is more severely judged than rape.