In a quirk of the league's complex playing-list and salary-cap rules, clubs must have at least three senior-list vacancies in order to take part in the national draft, which was held over two nights this week.
Clubs are increasingly opting to delist players to open up some of those spots, with the promise of re-selecting them through various drafts.
But occasionally the move backfires, as Gold Coast famously found out the hard way in 2021 when North Melbourne snapped up delisted utility Hugh Greenwood as a free agent before the Suns could re-draft him.
This time it was Gold Coast who pounced, selecting Knobel in Friday's rookie draft.
The 20-year-old ruckman didn't play a senior game in his two seasons with Fremantle, but had been promised a list spot for 2025.
The Dockers quickly signed a replacement, taking Claremont teenager Aiden Riddle to add depth to their ruck stocks.
Riddle was among the nine players without previous experience on an AFL list who were picked up in the rookie draft.
AFL Academy prospect Archer Day-Wicks was the first of them, joining Essendon at pick six.
Archer Day-Wicks (left) has been selected by Essendon at pick No.6 in the AFL rookie draft. (Joel Carrett/AAP PHOTOS)
Port Adelaide took Central District product Tom Cochrane, the son of former Power player Stuart, while Geelong added three fresh faces to their rookie list.
The Cats selected Geelong Falcons products Xavier Ivisic and Joe Pike, as well as Oakleigh Chargers midfielder Patrick Retschko.
Carlton selected GWV Rebels co-captain and best-and-fairest winner Harry Charleson, while former St Kilda defender Ben Paton was given a career lifeline by Sydney.
Only two picks were made in the pre-season draft, with triple-premiership forward Gunston rejoining Hawthorn, as expected.
Brisbane looked to add depth to their key-position stocks after the retirement of flag hero Joe Daniher by selecting former Gold Coast player Sam Day.
The Brisbane Lions have chosen former Gold Coast player Sam Day to bolster their attack. (Dave Hunt/AAP PHOTOS)
The 32-year-old played 155 games in 14 seasons with the Suns.
Chris Burgess, Harry Schoenberg (both Adelaide), Darcy Craven, Darragh Joyce (Brisbane), Ash Johnson, Oleg Markov (Collingwood), Josh Fahey, Lachlan Keeffe, Jacob Wehr (all GWS), Toby Pink (North Melbourne), Brad Crouch (St Kilda), Aaron Francis and Joel Hamling (both Sydney) all returned to their clubs through the rookie draft.
Former Geelong and Port Adelaide player Quinton Narkle did not nominate for the draft but is tipped to join Fremantle during the pre-season supplementary selection period, while ex-Lion Jaxon Prior could do the same at Essendon.
Former Carlton forward David Cunningham is also chasing a career lifeline over summer.
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