Director Norman Jewison said of this film's lead actor: "It's an unusual role for Al Pacino. In past films, like Dog Day Afternoon (1975) and even Serpico (1973), he's been the eccentric, cut off from a sane world. This time, he's the most rational person in the picture. It's everyone around him, and his environment, which is bizarre."
When Al Pacino was cast he had been considering the lead role in Kramer vs. Kramer (1979) which he rejected in order to do this movie. Ironically, when Pacino was Oscar nominated for the Best Actor Academy Award, Dustin Hoffman won for Kramer vs. Kramer (1979).
The closing courtroom scene was filmed on the first take.
During filming, actor Al Pacino frequently ad libbed and improvised. Pacino liked to do this because he was slow learning lines as well as to be spontaneous. This however can interfere with another actor's performance. Reportedly, Pacino's mentor, Lee Strasberg, said "Al, learn your lines, dollink!". Pacino years later recognized that this was good advice.
To prepare for his role as a lawyer, Al Pacino interviewed attorneys, researched the legal profession and attended court with legal eagles.