I just recently started messing around with a friend using D&D 5e, and the two of us have been goofing around in Roll20 with characters we made to test some things, one of which a 3rd level fighter who went Battle Master. I chose my maneuvers, and later was browsing opinions on which ones were good.
I saw that people tended to rate Rally okay to poor, one argument I saw being that there were more useful applications of a bonus action, like a Polearm Master's blunt strike. I've actually found Rally to be pretty nifty in my short time with it, as I realized that superiority dice come back after a short rest.
What I've been doing with it is blowing all of my superiority dice on Rallies before a short rest on our squishy party members because in the PHB there isn't a defined length of time that the temporary hit points last, which the PHB states means they last until you finish a long rest.
Problem is, are you even supposed to use maneuvers outside of battle? I didn't say anything saying you couldn't, I mean, you can cast spells outside of battle, but it does seem somewhat against the spirit of "maneuver" to use it in a non-combat situation. Am I just missing something somewhere?
Best Answer
Firstly, it is worth noting that (as Eidolon notes) temporary hitpoints do not stack (pg.198 PHB). That is to say, if you have 10 temporary hp, and gain 12, you now have 12, NOT 22.
Technically yes
With that in mind, as per this question, all actions that can be used in combat, can be used outside of combat. Combat is not special in that regard - it is just a way of resolving encounters in which the participants want to fight each other. So, RAW, maneuvers can be used outside of combat.
But a DM could reasonably disallow it
However, it could be argued by your DM that 'bolstering companions resolve' outside of combat is inneffectual as there is nothing around to damage their resolve. Hit points, including temporary hit points, represent not only physical strength and wounds, but also mental resolve. Gaining temporary hit points through rally represents having your mental resolve strengthened by an inspiring shout from the fighter. A DM might argue that, since 'rally' implies rallying characters from fear, this would only work in combat.
That said, I would be tempted (as a DM myself) to allow it on the basis that an inspirational speech before battle could bolster one's resolve. There is a reason why commanders of (e.g. ancient) armies gave speeches to their men before battle. Given that, as noted above, temporary hit points do not stack, this should not be too overpowered.