Officers called a flagrant foul on a 31-year-old Haverhill man who police say took a swing at Celtics point guard Rajon Rondo early yesterday during an appearance at a downtown [Lowell] dance hall. . . . Officer Michael Kandrotas noticed a scuffle, and learned that someone "took a fighting stance and threw a punch" at the Celtics all-star and his entourage, which included fellow NBA players Josh Smith of the Atlanta Hawks, former Celtic Nate Robinson and Rudy Gay of the Memphis Grizzlies.