WAGSTAFF

In 1957 the popular TV western Gunsmoke filmed an episode entitled "Buffalo Man", about a vicious buffalo skinner (John Anderson) who mistreats a young woman traveling with him.

Jack Klugman, fresh from 12 Angry Men, makes an early Hollywood appearance as the skinner's partner.

The episode's climax is a brutal (by 1957 TV standards) fistfight between Anderson and James Arness as Marshall Matt Dillon.

For some reason, the dailies (rushes) and outtakes from this episode were saved instead of being thrown out. You can see some of them here:

In 1959 this footage, or at least the climactic fight scene, was featured in an instructional film entitled Film Editing: Interpretation and Values, put out by the A.C.E. (American Cinema Editors), the Hollywood editors union. This film showed the Gunsmoke scene as cut by three editors, and explored the various differences in their cuts.

By the '80s and the film school boom these dailies were being used by many film programs for an editing exercise: use the various takes and different angles to create a re-edited scene. This is still being done; I found this project description from UNLV (the same institution where Ray Dennis Steckler – writer and director of Rat Pfink a Boo Boo and The Incredibly Strange Creatures Who Stopped Living and Became Mixed Up Zombies – was once a film professor, but that's another story):

UNLV film editing course

Many film students have uploaded their versions to YouTube:

Gunsmoke editing exercise

There have been all sorts of re-edits: music videos, Marshal Dillon made into the villain… I think this one is my favorite; it's not only funny but it's one of the few I've seen to recut the sound as well as the visuals: 

From IMDb's entry for actor John Anderson: 

The episode "Buffalo Man", climaxed with a brutal fistfight between his character, Ben Siple, and James Arness' Marshal Matt Dillon. This action scene, from its build-up to its dénouement, would become the common sequence upon which generations of budding editors would cut their teeth in film school. This sequence also features Jack Klugman, who would later co-star with Anderson in the classic "A Passage for Trumpet" episode of The Twilight Zone (1959). Shortly before his death, Anderson remarked that it was Klugman who informed him, many years after the filming of their Gunsmoke episode, that they had become legendary among film editors for their ubiquitous presence in student editing bays.