PORT Adelaide defender Tom Jonas has been handed a six-match ban for striking Andrew Gaff after the decision to challenge his charge backfired at the Tribunal on Tuesday night.

Jonas received the equal-largest suspension since Dean Solomon was handed an eight-match ban for striking Geelong captain Cameron Ling in 2008.

It was equal to Campbell Brown's six-match suspension for making forceful front-on contact to Adelaide's Aidan Riley in 2012.

Jonas, who had been referred directly to the Tribunal for his late hit on Gaff, chose to argue his case and sought to have the intent downgraded from intentional to careless.

His decision to challenge elements of the charge cost the defender his right to a one-match discount for an early guilty plea.

As he left the Adelaide hearing room on Tuesday night he said he would not seek to challenge the ban.

"I caused an injury to Andrew and let's not forget that … it's good that he's OK," Jonas said.

"The jury found that what I did was a six-week penalty and I accept that."

Jonas had earlier argued he didn't intend to strike Gaff but had been caught in two minds between bracing for contact and attempting to spoil as he closed in on the Eagles' midfielder during last Saturday's clash at Adelaide Oval.

The 25-year-old told the Tribunal he had taken the "soft option" of protecting himself and the forearm he raised was intended to protect his body from impact in the collision.

Jonas will spend seven weeks out of football, with the Power having a bye in round 14, returning against North Melbourne in round 17 at Etihad Stadium.

"One thing I'm sure of is I didn't intend to make contact with him like that," a contrite Jonas told the Tribunal.

"I regretted it immediately and I felt terrible.

"It's a little bit embarrassing. I took the soft option and was scared for my own safety.

"At no time during the incident did I have the intention of striking Andrew Gaff in the neck or head and hurting him."

Jonas's argument was dismissed by the jury of Hamish McIntosh, Shane Wakelin and Emmett Dunne, who deliberated for seven minutes before settling on their penalty.

The final ban was one-match shy of the seven-week penalty recommended by AFL counsel Jeff Gleeson, who accused Jonas of reconstructing the truth.

"It's a human response to convince yourself that you didn't intend to do what the evidence shows you did," Gleeson said in his case against Jonas.

He said the jury should reject the defender's evidence that he had intended to spoil and braced for contact at the last minute.

"That doesn't leave many other palatable alternatives ... at the last minute he intended to strike," Gleeson said.

Jonas did everything he could to express his regret and contrition, Tribunal chairman David Jones said, and had been aware of his mistake immediately.

Umpire Shane McInerney gave evidence that the defender had been "melancholy" when told he was on report and didn't attempt to plead his innocence on the spot like others players.

When giving evidence, Jonas admitted his actions had been a "clumsy mess".

"I expected I would only make contact with his back or shoulder," he said.

"I never intended to make contact with his head or neck."

Jonas said he spoke with Eagles Josh Kennedy and Nic Naitanui in the aftermath to check if Gaff was OK and sought the midfielder's phone number to apologise.

The Eagles' medical report stated that Gaff had been found unconscious and remained so for two minutes after the incident.

Gaff had suffered a "moderate severity neck injury from impact", and required physio treatment and medication for neck pain and headaches.

He missed three days of training and was expected to miss one match, according to the Eagles' doctors.

Jonas was represented in Adelaide by Mark Griffin QC, who said the defender's evidence was "consistent with a truthful account, not someone who has reconstructed the truth".

He pleaded with the jury not to tarnish Jonas with the same brush as "thugs", who have committed off-the-ball offences.

"This is not a Barry Hall punch," he said, in reference to the former Western Bulldogs, Sydney Swans and St Kilda goalkicker, who punched Brent Staker in 2008, earning a seven-match suspension.

Jonas will miss matches against Melbourne, Collingwood, the Western Bulldogs, Fremantle, Richmond and Hawthorn.