Bang to rights

[thebraveboy]

I know what it means but why bang, and why the odd word placing.

[Quizmonster]

The phrase started life as a piece of American criminal slang about 100 years ago, to mean 'caught in the act' or 'found in possession of' etc. In other words, there was no prospect of talking your way out of your guilt. The authorities were within their 'rights' to suspect you.

That probably developed from the much earlier use of 'bang' to mean 'exactly' or 'suffering a sudden shocking blow' or even just 'all of a sudden'. You see it in phrases such as "the ball landed bang in the middle of the net" or "the moment I get interested in something, bang goes my sleep".