A librarian at the Carnegie Library of Pittsburgh's Oakland branch was slightly injured Tuesday after a patron punched him, knocking him to the floor.

The man attacked senior librarian Barry Chad, 57, at 11:45 a.m. after Chad asked him to stop moving a chair from a microfilm area in the Pennsylvania Room on the second floor of the library at 4400 Forbes Ave., authorities said. The man had previously visited the library in the past month but has not been identified.

Witnesses said the assailant was black, about 30, about 6 feet 1 inch, about 160 pounds, with a mustache and short black hair and wearing a dark hooded sweat shirt printed with the words Mt. Lebanon Soccer, dark dress slacks and dark dress shoes.