Can someone explain the meaning / background of the phrase "contrary to form"?

I think it means something along the lines of "to break the status quo" or...?

Thank you.

It means that what someone has done is the opposite of what you would normally expect.
So for example if you know someone who is always late for appointments, but today he arrived on time you can say, "Contrary to form, he was on time."

I don't know if this is used outside the UK.

Isn't is a horse-racing analogy?

The form is a summary of a horse's ability, racing record, pedigree, etc., and an analysis of form will give one an idea of how well the horse will perform.

If the horse runs "contrary to form", then it will have done better, or worse, than its form would lead one to believe it should.

Interesting. Thanks gentlemen.

Hi, Buraian! If you are a new member, I hope you will stay with us to play with words. We meet for a "chat" at 6 pm Greenwich Mean Time, on Saturdays.

Welcome to Wordcraft, Buraian! Glad to see a new face!