Frederick played 14 games for the Power across his four years on the list, drafted through Port Adelaide's Next Generation Academy in 2018. The 22-year-old managed just six games at senior level in 2022.
Williams meanwhile, has played just one game at senior level since arriving at Port Adelaide with Pick 23 in the 2019 National Draft, with his debut coming in Round 15, 2021. The 21-year-old forward featured in all of Port's SANFL games this season, booting 20 majors.
Both McEntee and Dumont have been rewarded with new deals as the club continues to put faith in their development, with McEntee playing ten games since arriving at the club in the 2021 mid-season draft, while Dumont managed eight matches in his debut 2022 season for the Power after a eight year stint at North Melbourne.
Port Adelaide List Manager Jason Cripps extended his well wishes to Frederick after his delisting.
“Marty is a much loved player at our club who came through our Next Generation Academy program,” Cripps said.
“Unfortunately, we have reached the time of the year where we have to make tough decisions regarding the future of our list.
“After four years on our list, Marty was unable to establish himself as a consistent performer within our AFL team and we have had to make the difficult decision not to offer him a contract moving forward.
“We wish Marty all the best for the future and he will always be welcome here at Port Adelaide.”