Yes, there are people that are inspiring. They can convince people to fight for a cause, but once they are fighting I doubt they can make them fight any better. Certainly not on a blow by blow basis. Someone mentioned a boxing coach. Do you really thing a boxer is twice as effective if the coach is in the corner saying, "Hit him again! Hit him harder!" Really?
Yes, this happens. It doesn't happen in the way you've put it, but it certainly happens in combat sports.
Consider an MMA fight. There is a gameplan going in. You will hear a coach reiterating instructions to a fighter and that fighter, who is currently forgetting their gameplan and just reacting on instinct, will adjust in real time. And these aren't abstract instructions. You're talking about things like:
* Circle left, circle left, circle left (or right)!
* Underhooks, underhooks!
* Hip up, hip up!
* Watch the triangle, watch the triangle!
* Change levels, change levels!
* Lead left > double leg!
Etc, etc, etc. Corners aren't just shouting specific instructions to hear their own voices.
It happens in ball sports.
Consider basketball (effectively squad-based skirmish with 5 participants per squad, much more akin to D&D). I'm 38 and change. I've been playing this game since I was 4. I've played with an enormous number of players of varying athleticism, moxie, and instinct/IQ.
Those latter guys with a high level of moxie and/or instinct/IQ? Despite the fact that they may not have athletic parity with other players on the court, they are force-multipliers in the extreme...and not in some abstract, unable-to be quantified way (the W.A.R. stat in sports these days just that). They do things, in the very moment that improves the players they are playing with. You're talking about things like:
* Calling out picks, communicating them quickly and effectively to the guy getting screened and helping as needed.
* Seeing backscreens and backdoor plays before they manifest and effectively communicating them to remove the offense's potential competitive advantage.
* When in a zone defense, effectively communicating where offenders are cutting and making the zone vulnerable so an unaware teammate can recover (and often briefly covering for them).
* Quickly determining a teammate's deficiencies and an opponent's strengths/weaknesses and communicating how this competitive disadvantage can be mitigated (such as "force him to go left").
* Always hustling after (and typically winning) loose balls where the prospects of retaining/gaining possession are 50/50. This may even involve diving on the floor. This becomes infectious. You invariably see this shaming or inspiring (which is basically the same thing when it comes to utility) teammates to do the same.
* Guiding offensive traffic (cuts, guard-arounds, etc) and setting effective screens (back or ball screens) and eating the (often painful) contact to gain a competitive advantage for his teammates.
Etc, etc, etc. This happens in real time.
Extreme situational awareness and tactical acumen (which go along with the ability to process information staggeringly fast and effectively communicate it with mental shorthand so it triggers muscle memory) are major advantages. Except for with the most self-celebrating, narcissistic little me-first Bs (who are losers that you don't want anything to do with anyway), grit and cool are utterly infectious at an unconscious level (later you can appreciate it consciously).
Guys/gals that possess these traits, whether that be a particular noncoms in a war or a savvy vet on the court, are huge difference-makers for group efficiency/proficiency and morale both in real-time and during brief moments of down-time.