I have carried one ball on in each of the last 7 years.
One year, I asked at the ticket desk if I could carry it on, she said no. I said, well, I am going to take my chances. TSA let me through with no problems. Another year, I got mine through with no problems, and another guy in my group, went through at a different time and a different check point, was told he couldn't bring his on due to the "not be able to see through it" clause. He brought a buzzsaw silver diamond and I had my target zone.