The chase scene at PNC Park was filmed on August 22, 2010, during an actual game. The Pirates beat the Mets 2-1. John Singleton wanted to film a chase scene there, which was not in the script, with a small crew with Taylor Lautner doing his own stunts.
(Director Cameo) John Singleton, the director of this film can be seen on board the train wearing a tan shirt sitting in a booth when Karen goes to get food for her and Nathan. He is also seen again when Nathan enters the same room.
In the hospital scene when Nathan dials 911, he gives his address as 2009 Clearwater Drive. This is a possible reference to The Twilight Saga, which Taylor Lautner (Nathan) stars in; 2009 being the year that The Twilight Saga: New Moon was released in theaters and Clearwater being the surname of characters Harry, Seth and Leah who appear in the films.
Nathan wears a Pittsburgh Pirates shirt, #21 with the name Clemente on the back. Roberto Clemente was a star player for the Pirates. He was the first Latin American to have 3000 hits, and the first Latin American elected into the Hall of Fame, posthumously. He won 12 golden gloves, 15 All-star selections, lifetime .317 batting average, and played in two winning World Series, being MVP in the '71 series. He died on a flight to Nicaragua on the 31st of December, 1972, flying with emergency relief items to help after the earthquake there. The statue outside PNC park (which was possibly going to be named after Clemente before PNC bought the naming rights) - where Nathan leaves a ticket - is of Roberto Clemente.
When Nathan is taking Karen to the hospital, a firetruck is shown going the opposite way on the bridge, presumably headed towards the remains of Nathan's house. The camera then pans over a night shot of PNC Park, which alludes to the climactic confrontation between Nathan and Kozlow at PNC Park at the end of the film.