Williams, arguably Wales' most silky and penetrating strike runner, was ruled out of the tournament Friday after hurting his ankle in an accidental collision in training two days earlier. Halfpenny is back in the team after not even making the 23-man matchday squad for the 20-19 win over France in the quarterfinals.
"He is undoubtedly a big loss from an attacking perspective and what he has achieved in the game in the last year or so," Wales coach Warren Gatland said of Williams. "But bringing in the experience of someone like Leigh Halfpenny gives us a different element."
"He is defensively probably the best fullback in the world in terms of his aerial game and coverage." Gatland said he had a "long debate" over whether Halfpenny was going to start even before Williams' injury.
"It is a change," he said, "but we don't think that we are weakening the side in any way." Davies missed the win over France because of a knee injury but has trained all week. He replaced Owen Watkin, who dropped to the bench.
"He was very close last week," Gatland said, "and he made a decision last week to rule himself out for the betterment of the team." The other change to the team was the selection of Ross Moriarty at No. 8 following the tournament-ending hamstring injury sustained by Josh Navidi against France.
Wales team: Leigh Halfpenny, George North, Jonathan Davies, Hadleigh Parkes, Josh Adams, Dan Biggar, Gareth Davies; Ross Moriarty, Justin Tipuric, Aaron Wainwright, Alun Wyn Jones, Jake Ball, Tomas Francis, Wyn Jones. Reserves: Elliot Dee, Rhys Carre, Dillon Lewis, Adam Beard, Aaron Shingler, Tomos Williams, Rhys Patchell, Owen Watkin
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