Jose Rivera has walked through Crystal Park in western Lancaster daily for the past 10 years.
The 60-year-old lives nearby on Coral Street. Rivera has made it his mission to keep the park clean while getting to know everyone in the neighborhood.
On Sunday he went to the park after hearing that a sign he posted for an upcoming block party was torn down.
While there, someone attacked him, striking his face, Rivera said.
"I did not see it coming. Why should I be looking? I've known everyone in this neighborhood for 10 years," he said.
Rivera went to the hospital and was treated for "bumps and bruises" on his head and face, he said.
Rivera is a member of the Neighborhood Leaders Academy, a six-week training program to "identify and cultivate neighborhood leaders" in Lancaster, according to a post on the city's website.
Police confirmed that a man was assaulted in Crystal Park around 8:30 p.m. Sunday. The investigation is ongoing, police said.
There's a Lancaster Safety Coalition Camera at the entrance to the park at First and Crystal streets, according to a camera map.