“Ring of Fire,” 9 p.m., USA

One moment can change a person’s life.

That’s the message of “Ring of Fire: The Emile Griffith Story” (the documentary will be shown without commercial interruption, a first for USA).

“Ring of Fire” is ostensibly the tale of the six-time boxing champion. But it’s also largely about the moment on which Griffith’s career turned: the night he killed Benny Paret in the ring.

Paret and Griffith had split two previous title fights. Paret added fuel to the fire the third time around by calling Griffith “maricon” (a Latin epithet for gay) at the weigh-in for that fight. Although “Ring of Fire” never directly addresses the issue, Griffith long has been rumored to be gay, something not widely accepted in sports today, let alone in the early 1960s.

The documentary is more than the usual rise-and-fall story of an athlete. It tells about the aftermath of that 1962 night, not just on the gentle Griffith, who most say was never the same fighter again, but also on Paret’s widow, Lucille, and his young son, Benny Jr.

“Ring of Fire” is riveting, a modern-day tragedy. It’s a must-see for sports and movie fans alike.