Flyers given out by the venue management at my second and third ever gigs -- Aylesbury Friars, winter of 1980, Adam & the Ants and Killing Joke -- that beseech the punters to keep it calm, "keep it friendly".
Don't know if they gave these out the first-ever gig, The Slits, same venue, earlier in the year, but if they did I didn't keep it.
There was a lot of tension and aggro at gigs in those days. For someone new to concert-going, they could be pretty intense experiences, even if there was no trouble as such. Afterwards, you really knew you'd been through something, physically. The other thing was how painfully loud the music was. I don't think many venues back then knew how to do rock sound that was powerful without harshing people's ears. You did often feel damaged afterwards. Many a time a gig would ring on in your ears for a day or several afterwards.
Do you get violence at gigs nowadays? Or even tension? I doubt it. Probably a whole range of factors here (decline of music as a source of tribal identity: a lot of the conflict at gigs back then was between different subcultural armies of the U.K.). But in amongst those factors, fairly prominent is, I think, a fading away of music's role as a space in which people work stuff out of themselves; music as valve or vent, an outlet for antisocial impulses. (Anti-social is still a social energy, whereas asocial is anomic). We are suppressed and constrained in different ways, in an information society, and deal with it differently (imploded into the derive, the endless circulation, of online etc, with its various mechanisms for harnessing drive energy) . Perhaps it's games above all that have taken up the slack in terms of all that surplus energy / lower-cerebral-cortex impulses.
You don't seem to see as much vandalism these days either, interestingly.