They’re playing roshambo. No other context needed.
roshambo GIF on GIFER

GIFER
One of my friend’s kids said he and his friends always played roshambo to decide things. I stood in disbelief for a minute before asking if he knew what that meant. He said it was just rock paper scissors. And then I proceeded to educate him on what it really meant. Not by example though.
I am so confused by your comment, roshambo is rock-paper-scissors. mentalfloss.com/…/why-do-people-call-rock-paper-s…
Why Do People Call Rock-Paper-Scissors "Roshambo"?

The term is more commonly used on the West Coast, especially in northern California.

Mental Floss

Sack tapping is also called “nut tag”, “bag tag”, “sack whack”, “bell flicking” and “roshambo”, the last name coming from an episode of South Park that featured the practice.

seems like we have a lot to learn from a “no context” community

Sack tapping - sh.itjust.works

> It is also called “nut tag”, “bag tag”, “sack whack”, “bell flicking” and “roshambo”, the last name coming from an episode of South Park that featured the practice. > Sack tapping is a slang term for a game where a participant attacks, by slapping, tapping, punching, kicking, elbowing, twisting, or backhanding a victim’s testicles. The term derived from ‘sack’, slang that refers to the scrotum, and the activity is a form of groin attack. This sociological manifestation of bullying can result in severe testicular injury that may require amputation as the only form of treatment.