No, this isn't The Ring; the ring is a boxing ring. "One Round" Jack Sander is a boxer working at a carnival, taking on all comers. His girlfriend Mabel sells tickets to his fights. One day a tall man accepts the challenge, hops into the boxing ring, and shocks both Jack and Mabel by defeating Jack in four rounds. It turns out that the nattily dressed tall gentleman is Bob Corby (Ian Hunter) the heavyweight boxing champion of the world. Bob and his manager, spotting Jack as a real talent, give him a job as Bob's sparring partner.
However, at least part of the reason that Bob hired Jack was Bob's attraction to Mabel, which Mabel returns, even after she gets married to Jack. Jack's rise through the heavyweight ranks becomes bittersweet when Mabel leaves him for Bob. Eventually Jack winds up fighting Bob for both the title and his wife.
- Amusement Park: Where the story opens, as Jack is working as a take-all-comers boxer at an amusement park.
- Big Game: Jack winds up fighting Bob for the heavyweight title.
- The Cameo: Eugene Corri, a well-known referee in that era, appears as himself.
- Clothing Damage: The confrontation between Jack and Mabel ends in Jack angrily tearing at her dress, leaving Mabel in only her slip.
- Distracted by the Sexy: Jack nearly gets knocked out when the sight of Mabel at the championship bout distracts him, allowing Bob to connect with a right hook.
- Double-Meaning Title: The ring is a boxing ring, but it's also the wedding ring Jack gives Mabel, and the bracelet that Bob gives Mabel to wear on her upper arm.
- Early Installment Weirdness: Somewhat atypical for the Hitchcock canon. It's the only Sports Story he ever made. It's the only film he ever directed in which he got sole credit for the screenplay. It doesn't have the kind of plot elements usually found in Hitchcock—no crime, no murder, no one Wrongfully Accused, not a thriller (it's a simple Love Triangle drama). And he does not have a Creator Cameo; he was hit and miss with the cameos in his silent film days.
- The Flapper: Two flappers straight from central casting are shown doing what flappers do: wearing slinky dresses, drinking heavily, and dancing frantically at a party.
- Impairment Shot:
- Jack's trainer gets very drunk at Jack's wedding to Mabel. The film stretches and distorts to simulate his drunkenness.
- A more elaborate one comes near the end. Bob hits Jack with what should have been a knockout punch. A surrealistic sequences of circles, lights, and abstract lines symbolize Jack's reaction. Luckily, he's saved by the bell.
- Literal Metaphor: Mabel finally returns to Jack at the end, saying "I'm in your corner"...and she's actually in his corner, in the boxing ring, between rounds of his fight with Bob.
- Love Triangle: Mabel marries Jack but still finds herself powerfully attracted to Bob.
- Match Cut: Used many times for scene transitions. In one instance there's a shot of Jack clasping hands with Bob's manager as they agree on the job, followed by a cut to Bob clasping Mabel's hand as he slips the bracelet on her arm.
- Scenery Censor: As Jack is lying down on a table naked getting tended to by his trainer, the trainer is positioned to hide Jack's crotch.
- Sports Stories: A boxer rises to the top while losing his wife to his rival.
- Time Passes Montage: Jack's trainer points at a poster, which shows Bob's name on top in big letters as he's fighting a championship bout, and shows Jack's name in tiny letters on the bottom as the fourth undercard. The trainer remarks that Jack has a long way to go. Then a series of otherwise identical posters show Jack's name rising up and up and up as he progresses from nobody to championship contender.
- Your Cheating Heart: Mabel cheats on Jack and eventually leaves him for Bob.