Discovered the tag ball grab today, which matches penis grab in formatting. Makes for a nice setup here: holding penis/holding balls penis grab/ball grab
Now ball grab isn't nearly as widely used as ball fondling, which is why I'm hesitant to propose this alias, but for the above matching in definition/formatting, I think it'd be a nice change.
Though one thing I've noticed: there is a big difference in the sense of force between the words "grabbing" and "fondling". Grabbing seems more like "squeezing", while fondling seems more like "rubbing". So maybe they should be kept separate and just have a tag cleanup in ball_fondling to separate the two?
Edit: Also discovered ball tugging/ball stretching, which is definitely visually different from the act of ball fondling.
Updated