"I believe Blowing the man down has two referents....
[T]he 'Flash Packets' would relieve Jack Tar of his hard earned pay by fair means or foul, effectively striking the sailor down.
In a later period... the harsh discipline exacted by officers in striking men down is doubtless the referent."

So in "I'm a Flying-Fish sailor.... You've robbed a poor Dutchman...," the sailor is who? An officer?