This listserv is somewhat dormant at the moment, due to the nature of people moving into and out of the New Haven area. The current active pickup game in New Haven is organized by various Yale graduate students. You can receive emails/information regarding times/locations by signing up to their listserv at http://mailman.yale.edu/mailman/listinfo/ultimate . They are very welcoming and fun; it is generally a game geared towards recreational (i.e. fun) players.
Another good source for information about pickup games in CT is to be found at http://www.ctultimate.com .
In years prior to 2007, YDSF has served as the loose organization for pickup games in New Haven. Most pickup games were played at the Yale University Intramural Fields, at the intersection of Rt. 34 and Central Ave. Schedule tended to vary slightly with the seasons. "Yale Divinity School Frisbee" is the origin of the "YDSF" group name, as originally games were played (circa 1986) on a small, sloped, grassy field on the Div School quad.
If a YDSF-game is being organized, you will receive numerous emails from various people saying they will attend. There is no official single organizer for YDSF pickup games. On subscription to the list you'll receive a PDF file indicating the fields we play at - save that file, as it has directions to alternate field sites.