ST KILDA defender Jimmy Webster has received the longest AFL suspension in six years after copping a seven-game ban for his ugly bump on Jy Simpkin.

In a landmark case that put down a new marker in the AFL's bid to protect players from concussion, Webster pleaded guilty and threw himself at the mercy of the Tribunal.

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The AFL argued for an eight-game suspension, which St Kilda believed was "excessive and disproportionate in the circumstances".

After deliberating for an hour, the Tribunal panel decided Webster should miss seven games, meaning Webster will not be available for selection until St Kilda's round-eight match against North Melbourne.

St Kilda immediately confirmed they had accepted the sanction and would not challenge it via an appeal.

"I wish to reiterate my remorse and again apologise to Jy for my actions," Webster said after the hearing.

"I will take this time on the sidelines to reflect on my actions and work hard to keep it out of my game."

This ban is the biggest in the AFL since West Coast's Andrew Gaff was banned for eight games for breaking the jaw of Fremantle's Andrew Brayshaw with a behind-the-play punch in 2018.

Webster's action was graded by match review officer Michael Christian as careless conduct, severe impact and high contact.

St Kilda's lawyer Adrian Anderson, the AFL's former football operations boss, noted any previous bans of four games or more had been classed as intentional rather than careless.

"What is proposed is a massive, sudden shift in sanction that is out of whack with the evolution over time," Anderson said.

"There is a very significant line between intentional and careless.

"(Gaff's hit on Brayshaw) is in a different category.

"It’s not necessary to pick him (Webster) out and pick a sanction that is out of whack to get a message through."

Simpkin has already been ruled out of the Kangaroos' round-one game against Greater Western Sydney due to being in concussion protocols following the incident.

It was the third concussion the North's co-captain had suffered in the last 12 months.

The incident happened four days after Port Adelaide forward Sam Powell-Pepper received a four-game ban for a bump that concussed Adelaide defender Mark Keane.

Anderson compared Webster's conduct to Powell-Pepper, labelling them "very similar".

"We’re not saying it’s exactly the same, but it (Powell-Pepper) was the higher end of careless," he told the Tribunal.

A remorseful Webster, who admitted he was on a base-salary contract with the Saints and relied heavily on match payments, said he was "not proud" of the incident and his thoughts were with Simpkin.

"I understand how bad concussions are and the need to stamp them out of the game," Webster said.

"The first time I watched it back I felt pretty sick about it."

Webster, who had only been suspended once before during his 150-game AFL career, received character references from high-profile lawyer Jack Rush, a St Kilda board member, and former Saints coach Alan Richardson.

The incident prompted a fiery exchange between Kangaroos coach Alastair Clarkson and Webster and his St Kilda teammate Dougal Howard.

Clarkson has been issued a "please explain'' from the AFL over the confrontation and could face his own sanction.

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Speaking to AFL.com.au's Damian Barrett in an exclusive interview on Monday, Saints coach Ross Lyon conceded it was an "unacceptable" hit.

"There is real concern for Jy, and in the current environment coming a week after Sam Powell-Pepper (who received a four-match ban for a hit on Mark Keane), we understand it is going to be a significant ban and as a coach you don't want to lose one of your really good players, but you've got to pay a price and he understands that," he said.

"The bottom line is it was an unacceptable action on a footy field."

St Kilda begins its 2024 season against Geelong on March 16.