If you say this sarcastically I believe you think there are legitimate reasons to worry when seeing people running around in a park. Can you elaborate why that is?
First, the person I was responding to was talking about a college campus and not a park. Second, the ridiculous number of mass shootings that have occurred in schools in the past three decades including the one on the Virginia Tech campus.
If you see a bunch of people running around and hiding in a place that's not expected it's not a great idea to assume they're doing it for fun. Not with a sad history of gun toting lunatics shooting up public spaces.
This would have been less concerning a couple decades ago, but after Virgina Tech, more than 1 or 2 people suddenly running past me would cause me to make assumptions. Some "Capture the Flag Game in Progress" signs would be comforting in that situation.