Remember, the New York Giants played their home games at baseball stadiums for much of their history: the now-torn down Polo Grounds from 1925 to 1955, Yankee Stadium from 1956 to 1973. It's only from the 1976 season on that the Giants played in their own stadium (Giants Stadium at the Meadowlands complex in New Jersey).
Since the new Yankee Stadium has the same field dimensions as the old one, they can easily accommodate a football field there.