I don't know where the term "breaking balls" came from, but after watching this brutal video, I must assume it was derived from an unfortunate cricket injury from a time long ago when plastic cups didn't yet exist.
New Zealand cricket player Kane Williamson nearly received a free castration from an errant ball in his match against South Africa. The 86-mph throw nailed Williamson right in the bollocks so violently that it even cracked his cup. The squeamish trauma caused him to hold his most intimate of areas as he winced in pain and play was suspended.
South African cricketer Dale Steyn was responsible for the cup-breaking ball, but didn't seem the least bit contrite for his dangerous throw. He told the injured Williamson, "It looked like it hurt, but I'm not apologizing." Talk about adding insult to crotch-grabbing injury.
I love that the announcers have a lengthy conversation about the physics of how the shattering of an athletic supporter cup disperses the energy from the ball. The discussion is cut short when one of the announcers brings up the point that Williamson was lucky that his testicle flesh was not pinched in the snapped plastic. The discourse did not have a happy ending, but thankfully Williamson returned to the match with a new cup and an octave higher signing voice.