A "Rumbleweed" is what martial artists, particularly Brazilian Jiu-jitsu practitioners will recognize as a random hairball that goes rolling-by, like a tumbleweed, during training. The "Rumbleweed," is the accumulation of everyone's hair, from grappling "rumbling." And, somehow, it always ends-up in a ball, rolling around the mats.
"I don't think Professor swept the mats. That's the third "Rumbleweed," I've seen today!" "Hey, there goes a "Rumbleweed!"
by Valhalla MMA May 3, 2019