In early silents, action shots were filmed with cameras on stationary platforms recording the scene as it transpired. Efforts to use mobile cameras were initially resisted as being artificial. Even William S. Hart’s films, while full of action, mainly relied on stationary cameras. Eventually, though, the now common technique of running a camera on a car or on tracks beside the moving subject, often a racing horse, became necessary; thus the running insert (sometimes called the running close-up) was born—a running shot in which the camera moves at a comparable speed beside the subject.
Cameraman Sol Polito pioneered this technique in Ken Maynard silents by mounting several cameras on a car running beside the racing horses. Besides keeping up with the fast-moving scene, Polito was able to create close-ups of spectacular stunt work, showing the subjects’ facial expressions in action in such films as The Red Raiders (1927). Other effects pioneered in this film include running inserts of charging Indians, a stampede of covered wagons, and a shot of a cavalry charge, beginning at a distance and then, with the camera moving slowly backward, being overtaken by the charge for a breathtaking effect. Running inserts have become much more sophisticated since the early Westerns, but the basic principle remains the same.
Historical Dictionary of Westerns in Cinema. Paul Varner. 2012.