Why "balls-up" means "something badly botched or muddled"?

The word "balls" in this expression, and in so many other colloquial expressions, refers to testicles.

You'll have to wait for an Englishman for that one.

Well, why "up" causes a mess?

I always thought of it as being a humorous (and slightly crude) way to invoke the image of being upside-down. I just googled the etymology and it seems the origin is a bit unclear.

Why haven't I thought of this?

Balls-up, screw-up, ****-up

All similar phrases to mean the same thing. I think the last two are principally AmE, but well understood everywhere. There's no real logic behind any of them; just crude and deliberately ugly expressions to describe a very unsatisfactory situation.

To cock [something] up, to create or cause a cock-up, to go tits up.

We refer to sexual or excretory anatomy to express contempt. E.g.

Person 1: David Cameron is a nice man.
Person 2: Nice man my arse!

It's because the ladies have begun to object to the expression "tits up".

When you fall on your back you go tits up. If you fall on your front you go arse over tit.

Careful, Roger, you are mixing up a noun with an adjectival phrase.

Did JTT get hold of your password?

http://www.urbandictionary.com/define.php?term=balls%20up
An interesting possibility...

Ha! My remark was polite, positive, and helpful.

You're welcome.

Good reading.
Thank you Ceili.

A remote possibility I think. But an interesting subject.

I think it's remote as well. Flags have always been used to communicate at sea.

Not necessarily . . . not all ships would have a flag locker full of signal flags--in fact, one would not expect a merchant ship to have signal flags at all. Even naval vessels didn't always rely on flags. A common signal from one naval vessel to another would be a gun to leeward (the sound would not carry very far to windward) and the main topsail flapping free in the wind. The signal meant "strange sail in sight," and meant an unidentified warship which could be seen by the signalling ship, but not yet visible to the ship to which the signal was directed.

All sailing ships would have a carpenter, though, and running up set of wooden balls would be an hour's work.

EDIT: The "strange sail in sight" signal was often reinforced by the lining the rail with seamen pointing in the direction of the unidentified ship--a simple and unmistakable signal.

It sounds like the work of CANOE (the Committee to Ascribe a Naval Origin to Everything.)

Btw, the merchant ship I worked on had plenty of flags.

What is true in the late 20th century or early 21st century was not necessarily true in the 17th, 18th and 19th centuries. When most of your crew are illiterate and even your petty officers are only barely literate, it would be a bit much to expect them to use signal flags the way a signals midshipman on a warship would do. The "strange sail in sight" is nor apochryphal--that you may not know it certainly is not conclusive.