Green’s Dictionary of Slang

knock-over n.

[knock over v.]

1. (Aus.) a shock, a disappointment.

2. [1920s–30s] (US Und.) a police raid.

3. [1920s+] (US police) an armed robbery.

4. [1920s+] (Aus.) a substantial, if surprising, success.

5. [1970s] (US) an easy task.