VanishedOne: Offhand, I don't think I've ever heard 'ball up' used in that sense, only
'balls up'. Maybe it varies with geography.
ZFR: The way I heard it (from my English teacher, who's Indian), balls up is the noun (this game is turning into a complete balls-up), or an adjective (this is one balls-up game)
or third person singular present tense (it's my friend's fault; he balls up my game every time). The infinitive verb is "to ball up".
Maybe as you said it is a regional thing. I don't think I've come across it being used like in the example in your link ("He really ballsed up that paint work"). But then again I hear it rarely, so you're probably more accurate having lived in the UK longer then me.
. It says 'to ball up' is 'orig. and chiefly U.S.' It doesn't seem to recognise 'balls-up' as a verb at all, but has the noun as 'chiefly Brit.' and 'balls' as a verb on its own as 'Brit. slang.'