What a complete pile of shite that is. The miners certainly had a legitimate right to strike against their own employer, the NCB. Let's put aside the fact that Scargill tried to circumvent his own union's rulebook to attempt to get a national strike without a national ballot.
Orgreave however was owned by British Steel and therefore the miners had no business being there as it wasn't their employer. They'd been thwarted in their original purpose because there was sufficient coal at the coking plants and power stations to see out the strike, plus he'd got his timing wrong with the strike starting in the spring instead of autumn.
Their intention was to close the Orgreave plant, as had happened at Saltley in the previous strike. This would stop supplies of coal from reaching BSC's nearby plants and risked causing permanent damage to those plants and the jobs of the people who worked in them. That's why Scargill's opposite number in the Steel industry, Bill Sirs, refused to join the strike and why there was an agreement between the NUM & the ISTC to allow a minimum level of supplies to be delivered.
It is quite legitimate to withdraw your labour in order to hurt your own employer. But it's not legitimate to use force and intimidation to hurt other businesses and the jobs of the people who work in those.