I have the feeling that the Battle Master fighter's Evasive Footwork maneuver is extremely powerful even without getting really creative.
How long does the AC increase from the Battle Master fighter's Evasive Footwork maneuver last?
Does the Evasive Footwork maneuver provide the AC bonus for an infinite number of rounds, even if the character only moves 5 feet per round?
Per Jeremy Crawford, "The benefit of Evasive Footwork ends when your move ends. It doesn't last from turn to turn."
Also, "Evasive Footwork grants its AC bonus only during your current movement."
Once your turn ends, you are no longer moving and thus the +AC stops.
Evasive Footwork (PHB p74):
...[add] the number to your AC until you stop moving
Movement (PHB p190):
On your turn, you can move a distance up to your speed
Even if you run for 10 minutes straight, in respect to the game you can only move on your turn, so you stop moving at the end of your turn.
The AC bonus of Evasive Footwork lasts at most one turn. If you make an attack, it "breaks up your move" (PHB 190), ending the bonus, so it is only good against opportunity attacks.
All this makes it one of the weakest maneuvers.
The other posters are correct about the RAW rules on this one. However, from a DM standpoint I was always under the impression that because every turn you take in a round is happening simultaneously, and every round is seamlessly transitioning from when everyone has taken their turn, it stands to reason that you have not actually stopped moving. Mechanically you have but for all intents and purposes, your character never stopped.
I would argue (and have always ruled) that if you used at least half of your movement on every turn without doing something like attacking, interacting with objects etc.. then you should retain the benefits.
As long as you don't attack you could continue to use it as part of a continuous movement. It would be good for rushing against enemy missiles and in addition to opportunity attacks it would also work against those holding their fire.
