After looking through my copy of The Divine Comedy, I have found your answer: The attacking man is Gianni Schicchi, and his victim, Capocchio. I have copied for you lines 25-33 of Canto XXX, which the illustration accompanies.
"As I beheld two shadows pale and naked,
Who, biting in the manner ran along
That a boar does, when from the sty turned loose.
One to Capocchio came, and by the nape
Seized with its teeth his neck, so that in dragging
It made his belly scrape the solid bottom.
And the Aretine, who trembling had remained,
Said to me: "That mad sprite is Gianni Schicchi,
And raving goes thus harrying other people."
