Or did you think only wizards had balls?
Well, honestly, witches don't have balls (that I know of). These balls are to repel witches.
(Image of beautiful blue balls, courtesy of the Cambridge Folk Museum's Folklore collection.)
Yes, this month, I have mostly been considering local folklore, which has led me to read Enid Porter's The Folklore of East Anglia. She was curator of the curious Cambridge Folk Museum*, which has a small collection of the weird and wonderful folk cures. There are moles paws to treat rheumatism; an alternative was to swallow a live spider (which admittedly is harder to exhibit). Similarly eating a roasted or fried mouse to treat whooping cough, or to hold a live fish in your mouth.
I'm just glad nowadays we have vaccines and antibiotics.
*Witch balls in the Cambridge Folk Museum are in my list of favourite witch things. But they don't quite beat the witch in a bottle in the marvellous Pitt Rivers Museum in Oxford.