The Danza: In the first season, minor outlaw Martin is played by Martin West.
Dueling Works: The show was scheduled directly against the Colin Baker era of Doctor Who for the teatime-adventure audience... and, in what was seen as a major sign of that era's dubious quality, regularly trounced it in the ratings.
Fountain of Expies: Nasir led to the creation of similar characters in several subsequent Robin Hood retellings, either due to a desire to make the cast more ethnically diverse or just because the later creators assumed that he was a traditional character.
An on-set accident in which Robert Addie's horse clashed heads with Jeremy Bulloch during a take was included in the finished show, reframed as a deliberate Kick the Dog moment on Guy's part.
During the filming of the quarterstaff fight between Robert of Huntingdon and Little John, Clive Mantle accidentally really hit Jason Connery over the head. Again, the blow was included in the finished show.
De Rainault's assessment of Philip Mark as a "posturing catamite" was supposedly an ad lib.
There was supposed to be a fourth season but the series was discontinued. There were serious plans for this to include Guy killing Marion in order to ignite the final conflict. (Something which eventually did happen in the later BBC Robin Hood, to very controversial effect.)