The MTA's website says "a police investigation at the 14th Street-Union Square" had caused Woodlawn-bound 4 and Pelham Bay Park-bound 5 trains" to run "local from the Brooklyn Bridge-City Hall Station to the 42nd Street-Grand Central Station" (4/5 express service has since resumed, but with delays). According to some initial reports, the investigation was because a man was pinned by a northbound express train.
A reader wrote us, "I just got off the train at union square. I was coming off the uptown 6 and there was a woman crouched over at the 4,5. She was kneeling next to a man who was basically stuck between the platform and the train. The train was stopped and all you could see was the man's legs. The rest of his body was under the train. This was around, 115. The police were running over with medics and they were trying to figure out how to get him out." Yikes.
The victim, apparently a white male in his 40s, was removed to St. Vincent's Hospital in "post traumatic arrest." We'll update when we know more about his condition.