The Guardian’s report supports most of McKelvey’s article https://www.theguardian.com/us-news/2017/jun/08/portland-alt-right-rally-militia-member-police-arrest, and I don’t see any direct contradictions.
The fact that an armed civilian (“private security force”? What does that mean? Hired killer, mercenary, random white dude with a gun and some yellow tape who looks like the cops?) member of one protesting group was allowed to or asked for help by the Portland police, and did so, is not in dispute, nor that he committed violence (grabbing a civilian by the neck).
The “create opportunities for mass arrests of peaceful demonstrators” tactics by the Portland Police — ask people to clear one large area, not give them enough time to respond, start pushing them into a smaller and smaller space, then tell them that space is closed (or physically barricade it), not give them time to disperse, force them into another waiting police unit’s space and then arrest/detain/beat them — are common enough. The Oakland PD used them against Occupy Oakland (I know people who were hospitalised, and there have been judgements against the OPD) and as I witnessed, the SFPD also used them against Occupy activists and supporting members of the public.
In every one of these instances the violence is started by the cops. No cops, no violence. No member of the public is going to go up against a phalanx of heavily armed (guns, batons, sprays, tasers …), heavily trained and over-protected army rejects just spoiling for a fight.
Just once, I’d like to read of incidents in which the police have truly protected the public — corralled the violent white fascists into the permitted space, faced them, beaten them, arrested them and cracked open their skulls.