Bah, I’ve done several 5k runs wearing nothing but sneakers and shades. And I used to play soccer wearing boxers. As long as you’re not chafing, you’re fine.
It all depends on the dangleage of the scrotum as to whether the jockstrap is desireable or not. I’ve examined literally thousands of them in my day (don’t pity me, I’m very well-paid), and some would bang against the knees if not contained, while others don’t have any lateral movement at all.
It’s not fun. That’s why I wear underwear. So why in the hell would you want to wear a jockstrap instead of underwear?
Beats me. But I’m sure there’s a reason. Or at least there was a long time ago. Jocks without cups are pretty old fashioned I think. Maybe undies back in the day were not as tight or supportive as some undies today. Did tighty-whities always exist? Did undies always exist? If there was only boxer style underwear back in the day, I could see why a Jock Strap would have been useful and invented.
But nowadays. I think tight underwear serves the same purpose and is just as good.
Every guy I’ve ever examined had one hanging lower than the other. (Qadgop’s looked at more of 'em than I have, but I’m an unpaid volunteer scrotum-examiner. What you might call an amateur. A hobbyist. A part-time afficionado.)
Where do you run 5Ks nude?
Not only that, but a 5K is kinda puss. My huevos don’t hurt 'til at least 6K.
Really? I start hurting after a walk to the mailbox.
Couldn’t have put it better myself. I once played basketball wearing boxers under track pants - a mistake I am never going to repeat. Every time I sprinted or jumped I could feel them bouncing around, and eventually I literally caught my balls in a twist. Let’s just say it impaired my playing abilities temporarily. Briefs for me from now on, thank you very much. I must say, however, that I find the jock strap idea a little too confining - it’s perfectly possible to wear a cup with just briefs. Just a little $0.02 dropped in the lake. 
Wreck Beach, Vancouver. Google it yourself, or TubaDiva will chastise me 
I could never see the point in them, myself. They’re annoying and chafing. I ride my bicycle, ski, and play racquetball without a jock. When I did Tae Kwan Do, I didn’t wear a strap.
As an undergrad I had to wear a jock. Gym policy. I hated it, not only for the above reasons, but because I came down with an incredible fungus infection that took a long time to overcome. (I didn’t get it from my jock directly – that was a new one I bought – but I suspect the jock created an environment the fungus fund inviting).
“‘Cause out on the football, football field,
You can never tell where a heel can wield,
Singin’, do you wear your jock a lot.”
The Fugs, from Do You Like Boobs A Lot