It's a funny scene in a pretty dark movie. It is also a fairly accurate portrayal of most self defense classes, especially ones geared towards women. These classes tend to place a great deal of emphasis on the devastating power of the groin shot.
Are groin shots effective? In general, absolutely. In Burton Richardson's JKD Unlimited/ For Street Self Defense, we practice groin shots all the time. However, as Burton himself said in a recent instructional video, they are not foolproof. I always stress to students that groin shots hurt, but they are not death rays.
This same subject was addressed in the 1976 novel Promised Land by Robert B. Parker, featuring his iconic private eye Spenser. Spenser had just been kicked in the groin by a female martial artist. The kick did not have the desired effect...
"That kick was supposed to finish you right there."...wise words, Spenser. And true.
"I am a professional thug," I said.
"It shouldn't matter," she said, frowning in puzzlement. "A kick in the groin is a kick in the groin."
"Ever do that for real before?"
"I've put hours in on the mat."
"No, not instruction. Fighting. For real."
"No," she said. "But I wasn't scared. I did it right."
"Yeah, you did, but you got the wrong guy. One of the things that a kick in the groin will do is scare the kickee. Aside from the pain and all, it's not something he's used to and he cares about the area and tends to double over and freeze. But I've been kicked before and I know it hurts but it's not fatal. Not even to my love life. And so I can force myself through the pain."
I am not a "professional thug" or a tough guy by any stretch of the imagination. I'm a writer who likes cats, tea, and classical music. However, I've taken my fair share of groin shots. One of the worst was while I was stick sparring. My partner managed to accidentally hit me full-force in the groin with a stick. Foolishly, I was not wearing a cup. It hurt. Quite a bit. Yet I didn't fall to the ground moaning. To be honest, for a brief second I didn't feel pain as much as I felt rage and wanted to launch a full-on counter attack on my partner. I quelled that anger and didn't act on it, because I realized my partner didn't actually mean to hit my groin. But the point is that I could have acted on my anger and I could have worked through the pain. If a cat-loving writer can do that, than anyone can.
This doesn't mean that groin shots don't work. They often do. As Rory Miller discusses in his excellent Meditations on Violence, criminals are often not expecting violent resistance. And a kick to the groin is certainly a great form of violent resistance. Many times, perhaps even the majority of times, it will indeed stop a fight. However, you cannot count on it. Even a solid knee/kick/punch, etc to the groin to just magically end a confrontation. You must be ready to follow up with additional attacks quickly and effectively. Don't knee a would-be rapist in the nuts and wait to see what happens. Knee him again. And again. And then punch him in the face. And punch him again. And so on and so on until he is disoriented enough for you to run like hell.
So practice your groin shots. They do work. They certainly worked for Bobby Hill. Just be sure to practice you follow-up attacks as well.