"We couldn't play with that sort of friction so we just stopped playing and walked away." Jimmy Page said later. "That seemed to cool the police from running round sorting out the audience and when we went back on stage after five or ten minutes, there was no trouble. What we're finding so often on this tour of the States is that the relationship between police and audience are bad from the start. So, it ends up with us having to cool things down."
The battle of Pittsburgh has been part of a hair-raising first fortnight in Zeppelin's second exhausting tour of the States.
In Vancouver: where they played to 17,000, the group had to pay £600 for backstage damage to dressing rooms and buildings caused by over-zealous fans.
In the Deep South state of Georgia: long-haired Jimmy Page has been taunted by people in hotel lobbies with remarks like: "What kind of girl are you?" Robert Plant was asked: "Are you a boy or a girl"
In Los Angeles: after the show before 20,000 at the forum, 4,000 people hung around for half-an- hour after the show ended, hoping in vain for an encore.
Tired but exhilarated, Jimmy Page flew back to New York and talked over lunch of the remarkable Zeppelin experience so far on a tour that will cover about 30,000 miles and take him, Robert Plant, John Paul Jones and John Bonham on about 40 airplanes.
Jimmy was dejected about police discipline of crowds because it marred their enjoyment. "The police act tough with crowds out of fear but if they just left people alone and didn't get all worked up and scared, I'm sure nothing would happen.", he declared.
"I mean, you see a cop waving a stick and you get shaky - and how can we carry on playing when the cops are roaming among an apparently peaceful audience, anticipating trouble? That's what's happening."
In Boston, two people in wheelchairs who came to see the show rode down the gangway and some attendants didn't care a damn that they were incapacitated. "If you're not sitting in the seats you've been allocated, you can't stay in this hall," they told them. People get so nervous and worked up by anything out of the ordinary." Led Zeppelin are finding that the miserable truth about the States is that it is an uncool country, especially for young people who want to identify with their lifestyle and their music. Older people just don't understand the new music and the "now generation's" fresh attitudes.
And what they fear or don't understand, they oppose.
A girl in Baltimore asked me if she could come backstage and watch the show from there. I thought this was the usual line from a girl wanting to hang around with us. So I said "Why don't you sit in your seat and watch us?" She said: "Because last time at this place, the cops teargassed the place and I'm frightened of being out there."
"That's the sort of tension we keep finding. There's such a lack of understanding and trust between the audiences and the police."
Despite these hang-ups and Jimmy's dislike of American food, he and the group are enjoying their trek across the country which includes visits to Texas, Carolina, Florida and Utah as well as the major cities.
"The warm atmosphere and reaction at the end of each concert makes it all worthwhile - unless you get a nasty scene like a dig at your long hair between the hall and the hotel room, which often happens," said Jimmy.
One of the Zeppelin team of 10 travels three hours in advance of the group to each venue to check equipment, fix security and liaise with the hall officials.
They are on stage for at least two and a half hours at each show. There is no other act on the bill. "We go through a lot of changes in style during the act," said Jimmy. "It starts off quite progressively and then we do some quiet numbers featuring organ. It's the first time we've used organ over here and people like it.
"We're doing one number - a 12-bar progressive blues, Since I've Been Loving You - that will be featured on the next LP, which might as well be called Led Zeppelin III. Incidently, three quarters of the album is already done."
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