Kubrick began his career as an independent filmmaker when he made Day of the Fight. […] Deciding to revisit his work on his Prizefighter photo essay, Kubrick contacted the Cartier twins (Vincent Cartier was Walter’s manager) and quickly gained their co-operation. He spent time with them, followed their daily routine and then filmed it. […] Day of the Fight is remarkably accomplished for a first film. As well as the superb photography and framing, there are stylistic touches that show, in retrospect, that Kubrick had emerged fully formed as a filmmaker. […]
There is a sequence in Day of the Fight where the Cartier twins walk towards us and the camera moves backwards. This reverse tracking shot, as it is known, is one of Kubrick’s most recognisable camera movements and is used in every movie. It implies that the walker is thrusting, dynamic, decisive, in control and powerful. During the fight between Cartier and Bobby James, Kubrick threw his hand into the ring and filmed the punching from the point of view of the canvas. In contrast to the controlled, stately shots that are associated with him, Kubrick often used his journalistic training to shoot blind or to get opportunistic shots from unusual angles.

Paul Duncan, Stanley Kubrick: The Complete Films, Taschen, Cologne 2003