Because where are they going to go?The security guards on the field are meant to control crowd interactions in the stands if necessary. Once the guys crossed the lines, their goal is not to chase them down, but to wait until they get bored of whatever they're doing.That's why in American sports, you see these people run all over the place, chasing these miscreants down, cheering all the while, all on FoxSports InsertNameHere. Then it gets shown on SportsCenter later.In European sports, once its determined they don't mean any harm (and I assure you, if they did, they'd have been taken down), the goal is to maintain crowd control, get the miscreants off the field without spending too much energy, and then ban them for life from every soccer club in England. (And likely the whole of Europe.) And not to show them on TV. Which is why, you'll notice, they didn't pan aorund like some overjoyed american camera man focusing on streaker a trying to steal all the bases before fat security guard zed tackles him at home.It's a giant rectangle surrounded by police. Where are they going to go?