A cautionary tale on exactly that point:
One year, a team near me (not quite the closest - the next town) were doing quite well and I was unappointed on the weekend they played a County Cup semi-final at home, so I went and watched the game. Asked the home coach if I could relieve him of the burden of running the line, and he agreed. As with the Away side flagsman, I was of course a TJ rather than an AR.
Some time in the second half, all hell broke loose from a ruck 5m infield on my side. It started with an Away flanker putting a haymaker on an offside home flanker who was getting away with murder, and then escalated. The ref's view was obscured by the ruckers - some of whom were actually on their feet!
Ref dealt with it well - whistle, step back, observe who is running in from a distance, try to remember who threw the worst punches - until he decided to ask me what started it and whether a card was warranted. I was reluctant as I would be unable to write any report and his report could not really admit to approaching a TJ. Ref wanted to be able to get one from each side off for 10, so I gave him the number. It didn't go down well with the Away team, whose on TJ had a few people he wanted to report. Ref lost the goodwill of the Away side, and struggled to hold it together thereafter.