Billie Jean King surprise tennis appearance in Center City.

Center City (WPVI) -- Sports icon and tennis great Billie Jean King made a surprise appearance Thursday at a pop-up tennis event in Center City.

She even grabbed a racquet for a friendly doubles match.

The big event at 18th and market streets brought attention to the Philadelphia Freedoms professional team, which King founded.

Their first home match of the season is on July 19th at Hagan Arena on the campus of Saint Joe's University.