Paul posted a question as a comment and I thought it merited its own post:
"I've got a weird question for you.
What are your thoughts on men wearing cups?
was rolling tonight and I noticed my partners cup as I went to pass his
guard. Like, I thumped up against it and it kind of blocked my knee
(without it I wouldn't have thumped his junk but I may have passed his
guard). I'm pretty damned new to all of this, and I'm sure I can adjust
to that sort of thing, but it did seem to sort of interrupt the flow.
Moreso than the occasional indelicate moment which can be ignored, or if
need be apologized for.
No big deal, but I wondered how you feel
in regards to men wearing cups. I can imagine running into a guy
wearing a cup and how it changes the roll, perhaps good and bad.
I don't wear one, but maybe I will at some point.
I feel a woman who has the experience you do might be able to talk about how they affect your roll in ways that a man might not."
My first thought was, I wonder why he thinks a woman would have a different reaction to rolling with a cup-wearer than a man would? But then I reconsidered... maybe a cup could be viewed as a considerate way of putting one more layer of "stuff" between someone's stuff and my body?
But no, in my opinion, cups are unnecessary (for that reason at least) and worse, they are miserable for me to deal with on an opponent. They make it much much easier to finish an armbar for example, and it's partly for this reason that they are not legal equipment in IBJJF tournaments among others. If you can't wear it in competition, you shouldn't be practicing with it.
Now, not possessing balls, you might think it's pretty ballsy of me to say you don't need a cup in jiu jitsu... but here's why I have this opinion. Yes, I've had maybe 2-3 rolls (over about 6 years of training) where my foot slipped off a hip and grazed someone's privates. I've honestly truly never done a knee-through pass and had any shin/knee-and-groin connection. And I mean grazed, as in glanced, maybe caused a wince, but not connected with/struck/slammed/pushed etc.
On the other hand, I have been armbarred many, many times. I've been kneebarred a few times, too. I have been triangle choked and on the bottom of north-south and even had people take my back. In every one of these circumstances, I would have potentially suffered a great deal more pain and discomfort from someone wearing a cup.
When I am rolling, I am not aware of someone's privates except insofar as I need to keep my hands, feet, knees, and other bits from using that one area of their body for leverage. If they're sitting on my face to finish a kimura, the last thing I am thinking about is their testicles. But, if I feel someone wearing a cup during a roll? depending on how I discover this, I will continue the roll and then gracefully decline another (and explain why) or I will stop in the middle and not continue.
So, the bottom line: please do not wear a cup.
Other people have written on this topic, too:
Jiu Jitsu Sweep