I don't have any references, sorry. I did some looking, and I could not find any viable intel.
For what it's worth, I'm a guy, and here is why I grab my crotch:
1. It's a comfortable feeling
2. Women can't enjoy the simple pleasure of crotch holding
3. It's funny to see who looks at your crotch when you do it
4. It's a good reminder to yourself of what your working with
5. It informs people that you have active reproductive organs
6. Sometimes you may have to reposition your goods to avoid uncomfortable situations (such as sitting on them)
7. Itches do occur and are most unpleasant
8. Doctors do it to multiple men a day, and I don't need a PHD to do it to myself
9. The pros out weight the cons
On a more serious note, and more sexual.
To my understanding a commonly accepted theory on this issue is that men do it because it's their way of asserting the manhood they know they lack to one another. This goes hand-in-hand with sexual insecurities. So in a nutshell... crotch grabbing only applies to men who either have a legitimate itch, or are trying to overcompensate.