Answer: The conflict between Cardinal Richelieu's guards and the Three Musketeers consisted of a duel fight. D'Artagnan tripped with the three musketeers and they decided to challenge themselves. The cardinal's guards arrested them because of a policy against duels.
Explanation: When D'Artagnan, a poor man from Gascony, is writing a letter of introduction, he sees the person who robbed him through the window. He starts chasing him, and in his way, he accidentally hits the three musketeers. They start a duel due to this incident, and the cardinal's guards arrive to arrest everyone, since duels are prohibited in that place.
