a) "the provocation". This may be real, as in Oldham, where unpleasant Stoke City supporters abused and (probably) assaulted people on their way to Boundary Park, or imaginary, as in the non-existent "BNP rally" which was the ostensible reason for the 'big' Bradford riot (the earlier Bradford riot had a real trigger). In the case of the Brum trouble the provocation seems to have been a bunch of white guys leaping about and giving it the "come on then" from the far side of a pretty large police cordon. Eventually the police chased them off. Why they didn't quickly surround and arrest the two or three chief offenders I don't know - given the circumstances, "conduct likely to cause a breach of the peace" would seem a reasonable charge. But the chasing off only started once missiles were coming over the cordon.
b) the response. Mostly if not always disproportionate to the ostensible provocation. Where the police still control the streets, takes the form of random, opportunistic attacks on whites, with at the most a bit of robbery 'on the side'. Where control is compromised, arson and looting are also prominent.
"me and twos move down new street, as some possible skin heads, possibly just drunk guys come up mouthing off, the protesting mob goes crazy and starts throwing missiles so shoppers scatter while the police chase them down the street then turn on the rest of us taking cover in the alley, while one guy is struck on the head with a brick"
c) the reporting. Without actually stating so, the reporting will give the impression that injured victims were casualties of 'clashes' or 'fighting' - with the implication that it's six of one and half a dozen of the other. In fact, many if not the majority of casualties are victims of racist gang attacks - for what else can you call half a dozen onto one ?
Let's look at the Mail and Telegraph coverage of Brum - not exactly the left-wing press :
But apart from one chap with a Union Flag getting attacked, having it torn from him and burned, rival protesters didn't clash - and a good thing too.
Mass brawl between right-wing group and anti-fascists as race riots spill onto streets of Birmingham
Down on his knees as his attackers' feet fly in, this man's face was left a bloodied mess. It was just one of the sickening scenes photographed when a riot erupted in a city centre after Right-wing protesters clashed with anti-fascist demonstrators.
But there wasn't a mass brawl, and the guy in the green shirt just happened to be in the wrong place with the wrong skin colour (and the guy with the Union Flag who was attacked is shown in another photograph, minus flag, speaking to police. Caption : "Trouble brewing: A man appears to argue with police officers").
If this is the narrative the Mail and Telegraph are handing out, don't look for much from the BBC and Guardian. If the green shirt guy had been Asian being attacked by whites, the "English Defence League" would now be proscribed by law and the victim would be on the news 24/7.