In Italy these professional condottiere evolved a scheme of warfare that practically eliminated bloodshed for a time. There were fights, yes -splendid, clashing, colorful affairs like vast tournaments- bu the contestants were covered in plate armor that prevented them from getting badly hurt, and the men they were fighting against -other professional like themselves- might well become their comrades-in-arms the day after the fight. […]
But when hand-guns began to be used, things were different. In 1439 the army in the pay of Bologna used hand-guns against a force in the pay of Venice, actually killing many of the Venetians’ knights. The Venetian army was so infuriated, it won the battle and rounded up the Bolognese army. Then the Venetians massacred the hand-gun men who had stooped so low as to use this ‘cruel and cowardly innovation, gunpowder.’ Why, they said, if this sort of thing were allowed to happen, war would become a positively dangerous business.
Source: Ewart Oakeshott, “A knight and his weapons” (1964), reprinted 2008, pag 103-104
I don’t know about what battle is he talking, but the next year (1440) the battle of Anghiari was fought, and only one man died… when he fell from his horse.