Cricket, biology and childbirth.

I was at a cricket match, and witnessed a batsman being hit in the box (area of the male reproductive organs), by a very fast ball (made of wood covered with leather). Most male spectators suddenly crossed their legs and winced, as I did. Many males witnessing this, feel physical discomfort, for a very short time, in the "box" area. Why is this? After all, when one witnesses a shooting, or other violence on TV/movies, it has no effect. Do women feel a discomfort when they witness childbirth? Thanks to all.