When was the dagger vs the pugio used

[Felix]

Actually, there is an account of the battle of Nicopolis in 1396, which specifically talks about men choosing to switch to daggers. The Crusaders had charged into a mass of Turkish infantry, and the press was so great that it was hard to effectively use a long horseman's sword. The knights were told to switch to daggers, which could be used in these very tight quarters, and did manage to cut through the enemy mass.

(there were more Turks after that, and the Crusaders were defeated, but the men at the time didn't know this would happen.)