What is the meaning of the Yellow balls in the second episode of Denki-Gai? One of the events of the episode is rolling a huge yellow ball. Hiotan is chosen to represent Umanohone, and there is some gag I did not get by that part.

What is the yellow ball supposed to represent?

Why is Hiotan embarassed and obviously aroused by the balls?

Why Hiotan says she can't be a bride anymore, after being trampled by one of the balls?
The balls were meant to be golden. In Japanese, "golden ball" is kintama, which is also slang for testicles according to Urban Dictionary. That's why the girls were so uncomfortable with this metaphor.