When sidekicks or minor supporting character contributes very little in brawls
Your hero is the main character; the one your audience wants to hear about. So it makes sense to highlight his feats of prowess in a fight scene, just to show how much of a badass he really is, right? But wait! What about the hero's minor ally? They're in the fight too. So how do you show a sidekick involved in the fight without taking the spotlight away from the hero? Simple! Just have him (or her) be indisposed for the duration of the fight. The method of being indisposed varies but typically, the fight will have either the sidekick fighting only one Mook and being distracted by that mook for the whole fight. Or...the sidekick is knocked off the balcony/ship/cliff that the fight is taking place on and, thus, spends the whole fight hanging on for dear life and attempting to climb back up to rejoin the action.
Examples of this trope include...Anime and Manga