Back in the late 90s, I was playing rugby in Missouri and simultaneously played flag football on my unit's team. I played center on FF and almost always over-aggressively grabbed the shorts at the waist on the quarterback in an attempt for the flag. Sometimes, I'd have cloth in my fingernails. They were definitely not rugby shorts quality.
How about having an urge to ruck when the runner is coming towards you?
I know this is an old thread, but along these lines, we're new team trying to form here in Denver. We usually practice on the opposite end of the park from the flag-football league. But next weekend we're going to practice next to them, in the hopes of recruiting some guys who want to loose the flags and play full contact.