A man was killed early Thursday at an Oklahoma City skate park, police said, making it the city's 20th homicide of the year.The man, whose identity has not been released, was killed around 3:10 a.m. at the park, 1700 S. Robinson. According to police, a person flagged down an officer regarding an injured person at the skate park. When officers found the man, he had a significant head injury, police said. They transported him to OU Medical Center, where he died from the injury.Police said they are working to figure out what led to the man's injury and death. No arrests have been made as of Thursday evening.