In 1972, Greenwood joined the staff of
Avalon Hill Game Company as Research & Design Director, as well as Editor of the company's house organ,
The General. Greenwood was also responsible for resurrecting older games and revising the rules to produce a new edition. His first assignment was to rewrite
Jim Dunnigan's rules for the unpublished game
Outdoor Survival; once he was finished, the game became a perennial bestseller for Avalon Hill. Other games Greenwood produced new editions of included
Anzio,
Afrika Korps, and
Caesar: Epic Battle of Alesia. Greenwood helped to organize the first
Origins Game Fair in Baltimore in 1975, and suggested calling the event "Origins" as a nod to Avalon Hill's creation of board wargaming. Greenwood also helped to organize the first Avaloncon, which morphed into the
World Boardgaming Championships, and was president of the
Boardgame Players Association. ==After Avalon Hill==