Woods' performance as Greg Powell was the film's most widely praised element, earning the actor a Kansas City Film Critics Circle Award and his first Golden Globe nomination.
Hollywood, Saturday, March 9th, 1963: LAPD detectives Karl Hettinger (Savage) and Ian Campbell (Danson) are kidnapped by criminals Greg Powell (Woods) and Jimmy "Youngblood" Smith (Seales). They are driven to an onion field near Bakersfield, where Campbell is shot and killed before Hettinger narrowly escapes as a cloud passes in front of the moon, plunging the onion field into darkness.
Hettinger's eyewitness account leads to the arrest of the two men, who are tried and convicted of first-degree murder. While they languish on death row, Powell and Smith learn how to exploit the legal system and after a series of appeals their sentences are reduced to life imprisonment following a court decision abolishing executions in California.
Meanwhile, Hettinger's physical condition and emotional state slowly deteriorate as his failure to act more aggressively on the night of the incident is questioned by those in authority and his fellow officers. Wracked with guilt and remorse, he experiences nightmares, impotence, weight loss, kleptomania, and thoughts of suicide.John Savage as Karl Hettinger
James Woods as Gregory Powell
Franklyn Seales as Jimmy Smith
Ted Danson as Ian Campbell
Ronny Cox as Sgt. Pierce Brooks
David Huffman as District Attorney Phil Halpin
Christopher Lloyd as Jailhouse lawyer
Dianne Hull as Helen Hettinger
Priscilla Pointer as Chrissie Campbell
K Callan as Mrs. Powell
Sandy McPeak as Mr. Powell
Lillian Randolph as Nana, Jimmy's Grandma
Steve Conte as prison guard
The film was shot on location in Valencia, Los Angeles, Maricopa, and Taft in California. A courtroom of the Superior Court of Los Angeles County was used for the trial scenes. The jury panel was taken to an onion field in Valencia to inspect it as a replica of the scene of the crime.
The Onion Field premiered at the Toronto International Film Festival on September 7, 1979, before opening in New York City on September 19. Wambaugh himself helped produce the film and choose the people who would work on it, including actor Ted Danson, who made his big-screen debut. Wambaugh reportedly was determined to make a film superior to the 1977 one adapted from his novel The Choirboys, the script for which was done by another writer. Wambaugh sued the makers of The Choirboys and got his name removed from the credits.
The movie opened to positive praise as a true story of justice mishandled. Janet Maslin of The New York Times observed, "This is a strong, affecting story but it's also a straggly one, populated by tangential figures and parallel plotlines. The criminals' histories are every bit as convoluted and fascinating as those of the policemen they abducted. Even the courtroom drama is unusually complicated, introducing a new legal team with each new trial.... The film is generally crisp and at times exciting, but it's also full of incidents that are only sketchily explained, and minus the all-important narrative thread that might have provided a clear point of view."
Variety called the film "a highly detailed dramatization" and said James Woods "is chillingly effective, creating a flakiness in the character that exudes the danger of a live wire near a puddle."
Time Out London thought the film was "expertly performed" and added, "It's the usual heavy Wambaugh brew: police procedure closely observed without a trace of romanticism, suggesting simply that life in the force is psychological hell. So far, so good. But that very insistence on authenticity is followed by the film to the detriment of the narrative's dramatic structure; half way through, the whole thing begins to ramble badly. Engrossingly sordid, nevertheless."
MGM Home Entertainment released the Region 1 DVD on September 17, 2002. The film is in anamorphic widescreen format with an audio track in English and subtitles in English, Spanish, and French. Bonus features include commentary by director Harold Becker and a featurette about the making of the film.