Green’s Dictionary of Slang

directly, forcefully.

1930		J.P. McEvoy Hollywood Girl 86: That’s a laugh isn’t that a wow now we cut to the chase she’s after him he’s after her he hides behind a tree she runs into it socko.
1934		T. Minehan Boy and Girl Tramps of America (1976) 137: I’m high-tailing up State Street feeling kinda light in the head, and socko, I’m in the gutter.