Hartlett briefly left the field after the head knock during the second quarter of last week’s loss to Hawthorn at Adelaide Oval, but quickly returned to the fray. Port had already lost midfielder Brad Ebert, who was hospitalised with a bruised lung after a knock to the ribs in a heavy fall.

Ebert has been ruled out of tomorrow’s do-or-die clash with North Melbourne, but Hartlett has been named to play.

But the league, which has emphasised clubs’ duty of care to players on concussion-related injuries in recent times, subsequently sought a “please explain” from Port as to why Hartlett had returned to the field and played out the game.

This morning, the AFL announced it had hit the club with a $20,000 sanction over the incident, with half of the fine suspended until the end of next season.

The AFL’s General Manager of Football Operations, Mark Evans, said that after receiving a written explanation from the club, speaking to staff and examining match day vision “it was the AFL view Port Adelaide had breached regulations”.

In a statement, the AFL said the club doctor “noted symptoms and/or signs in Hamish Hartlett that necessitated his removal from play, to undergo a Head Injury Assessment, including a SCAT3 test”.

But Port “did not notify the AFL Interchange Official that a Head Injury Assessment was being undertaken”.

“Consequently, the AFL Interchange Official was unable to record the time required for the player to be excluded from the game [and] the player returned to the game after approximately five minutes, well before the 15-minute exclusion period had elapsed”.

“The period of exclusion would have provided additional time for the club doctor to be provided with vision of the incident to review the head knock, as required by the Head Injury Assessment Form,” the league found.

Evans said he took into account that medical staff were also concurrently “managing another significant player injury (Ebert) in the change rooms”.

Hartlett said this week that he “obviously copped a pretty heavy knock”.

“But I went through all the concussion protocol down on the bench… I did all the testing, no worries,” he said.

“And I got the all clear from the doctor – and I felt fine to go out and play and played out the rest of the game no worries.”

Port’s General Manager of Football, Chris Davies, said in a statement the club accepted “that although the concussion assessment was administered correctly, the club’s medical team erred in not notifying the AFL Interchange steward that a Head Injury Assessment was being undertaken”.

“If we had followed that protocol, Hartlett would have been excluded from play for longer so vision of the incident could be reviewed,” Davies said.

“Despite this issue of timing, Hamish was cleared of concussion at the time and has shown no sign of concussion during subsequent testing throughout this week… the club welcomes the AFL’s strong focus on protecting players from head injuries and our medicos’ sole concern was for the wellbeing of Hamish throughout the incident.”

The issue of concussion was highlighted this season with 22-year-old SA-born Brisbane Lions defender Justin Clarke forced into an early retirement after suffering a head-knock during pre-season training.