Why do the Friar and the Summoner get into a fight?

The Friar laughs to hear everything that the Wife has said, commenting that it is a “long preamble of a tale” (a long prologue to a tale) – and when the Summoner hears the Friar’s voice, he attacks him, commenting that friars are notorious for their long-windedness, telling him to “go sit doun!”. The Friar promises, in revenge, to tell a tale about a summoner to make everyone laugh. The Host quiets them down, and encourages the Wife to tell her tale.

"Overall, the narrator seems to harbor much more hostility for the ecclesiastical officials (the Summoner and the Pardoner) than he does for the clerics. For example, the Monk and the Pardoner possess several traits in common, but the narrator presents them in very different ways. The narrator remembers the shiny baldness of the Monk’s head, which suggests that the Monk may have ridden without a hood, but the narrator uses the fact that the Pardoner rides without a hood as proof of his shallow character. The Monk and the Pardoner both give their own opinions of themselves to the narrator—the narrator affirms the Monk’s words by repeating them, and his own response, but the narrator mocks the Pardoner for his opinion of himself."