After Odysseus and his men blind the Cyclops, they sail away from the island. Just as it seems they are going to get away, Odysseus shouts back to Polyphemus, taunting the monster and telling the monster his real name. In his terrible pride, Odysseus confirms his identity so that Polyphemus can tell people who bested him. It doesn't seem to occur to Odysseus that his identity could ever be used against him, but this is exactly what Polyphemus does. He prays to his father—the god of the sea, Poseidon—saying,
"Here me, thou girder of the land, dark-haired Poseidon! If I am truly thine, and thou art called my father, vouchsafe no coming home to this Odysseus, spoiler of cities, Laertes' son, whose home is Ithaca."
Further, Polyphemus prays that if Odysseus is fated to return to his home in Ithaca that he does so without any of his crew remaining, in a stranger's ship, and that he finds trouble when he gets there. In other words, then, Polyphemus asks Poseidon to exact revenge for the injuries done to him by Odysseus.