Rudolf Augstein reports another reason for the meaning of Bar-Abbas. It is not so probable as the Best Explanation in circulation (about which I don't admit no kind of reply, so much I am persuaded about his sound truth):
Jesus Bar-nash ----> Jesus Bar-bash -----> Jesus Barabbas
According this less probable hypothesis, the comparison was originally between Jesus Son of Man and Jesus called Christ.
"Mark" being a pauline, couldn't accept the intruder called Jesus Son of Man (the expression "Son of Man" is totally absent and unknown in Paul, just as Paul didn't know John the Baptist).
Hence in the original pauline proto-Mark, there was no "Son of Man" prophecies.
He attacked the Jesus Son of Man tradition, reducing him to a mere bastard criminal.
Jesus Bar-nash ----> Jesus Bar-bash -----> Jesus Bar-Abbas
Jesus Bar-nash ----> Jesus Bar-bash -----> Jesus Bar-Abbas
Nihil enim in speciem fallacius est quam prava religio. -Liv. xxxix. 16.