I think my match day experience may have some small relevance to the awful attack on the Luton Town supporter.
The match for my wife and I was spoilt by the heavy and heavy-handed police presence. With about 15 minutes to go before kick off, the road to our South Africa Road entrance was blocked off by the police and we were redirected elsewhere. We went the way we were told and the police there wouldn't let us through either and wanted us to go back to where we had just come from! The police told us they didn't know why we were being stopped and they didn't know which alternative way we should try. Instead we went back towards the Uxbridge Road to try another road up towards the ground where we joined a group of several hundred QPR fans being held up. Tempers were getting frayed and I think the police were actually making matters worse. At one point, the crowd were angrily chanting "you don't know what you're doing" and never has such a comment been more valid. We tried two more routes before finding a way in and arrived 6 minutes after kick off.
At the end of the match, we felt we ought to leave early (on 85 minutes) to avoid any trouble. Despite things being quiet, the police insisted on redirecting us into the White City Estate, completely the wrong direction to get back to our car. Obviously, as a 68-year old couple we looked more threatening than the Keystone Cops were prepared to engage with.
It may be my failing memory but I can't recall such a large and active police presence at a QPR match and I've been going since the 1960's. I thought we had left behind this sort of experience back in those days. If the police anticipate trouble and want to plan their response, I would expect them, at a minimum, to decide which roads to block and which alternative way to direct home fans. Well, they got that 50% right and it's a sad reflection on their competence.