When Spenser and Hawk check in with the desk clerk at the condo the witness is staying at in Promised Land (the series pilot) is reading Wilderness a non-Spenser novel by Robert B Parker, who created the Spenser character.
Sgt. Belson says Spenser had 4 years in the Boston PD. In the books he was actually a state trooper.
Chuck Connors was no stranger to the Celtics. He played with the Celtics in the 1946 1947 season. First player to break the backboard.