So the famous "walk" scene was spontaneous and improvised? Hmm...

The climactic walk in THE WILD BUNCH was not "spontaneous." But in the accurate sense that the sequence was conceived, staged, performed, and filmed, despite not having appeared in the screenplay, it was improvised. (Similarly, the bunch's exit from Angel's village also had not been planned; but director, cast, and crew shot it in a single afternoon because, as Sam Peckinpah later stated, suddenly he knew the picture needed it.)

Actors in theater might improvise an entire scene onstage -- but movies and the stage are completely different crafts. Most great films are constructed not shot by shot, so much as sequence by sequence. The WILD BUNCH walk sequence was born of Peckinpah's inspiration on a Mexican movie location, but no one would seriously claim that it was "done totally on the fly" (Not in the sense that you mean.)

After envisioning that unscripted action and its potential value to the final production, Peckinpah had to convey his intentions to his crew, key personnel, and principal cast -- so that the scene could be properly lit, the action rehearsed to the director's satisfaction, then performed by cast and extras, and effectively photographed: requiring multiple angles of the bunch (viewed from ahead and from behind), and their own point of view, shot with both standard and telephoto lenses (the latter adding to some shots a dramatically brilliant sense of "crowding"). All that power was amplified in the editing stage.

So, whynotwriteme -- that footage resulted from extensive imagination, preparation, and hard work. But if, as has been asserted for decades by multiple parties involved with THE WILD BUNCH, that dynamic walk never appeared within the written script before it was filmed ... then the sequence was improvised.

Most great films deserve a more appreciative audience than they get.