St Kilda ruckman Justin Koschitzke had his AFL comeback halted through suspension after his perennial bad luck followed him into a ruck duel.

Koschitzke was suspended for one game for making negligent contact with field umpire Josh Krull during the first quarter of the VFL reserves game between the Casey Scorpions and Williamstown.

The verdict means he must wait at least another week before he returns to the AFL after he suffered a fractured skull against the Western Bulldogs in round six.

Although the 23-year-old pleaded guilty, the VFL tribunal ruled it had a duty of care to protect umpires from players who were unaware of where umpires were positioned.

But Koschitzke's suspension brought into question disparity in umpiring protocols in the AFL and VFL, as the Saints star argued he did not know Krull would back out towards him when he charged in to contest a ball-up.

Under VFL rules umpires back out of bounces and ball-ups to the middle of the ground, whereas in the AFL umpires back out towards the boundary once they re-start play.

The tribunal ruled Koschitzke made "quite severe" contact into the back of Krull, which left the umpire with a sore head, legs and back, and left him in discomfort for the rest of the game.

"We are conscious you suffered a serious injury recently and that is bad luck," tribunal chairman Tim Robinson told Koschitzke.

"But we are very conscious about protecting umpires, especially from players who are rushing in to contest a ball-up and are not conscious of their obligation towards umpires."

Koschitzke admitted he did not see Krull in his way when he ran in and told the tribunal he was "extremely sorry" for making contact.

The tribunal rejected player advocate Sean Carroll's call for Koschitzke to be fined instead of suspended.

The Saint was fined $2,400 in the AFL last year for making similar contact to an umpire in a game against Geelong.

St Kilda assistant coach Matt Rendell admitted Koschitzke should have known where the umpire was positioned regardless of the different protocols.

"The players have still got a duty of care no matter where the umpires are on the ground and he probably should have seen him," Rendell said.

"He rushed to the contest ... he looked where his opponent was and just didn't realise where the umpire was.

"Now he might have expected the umpire to back out the other way (towards the boundary) because they normally do in the AFL, or have for the past two or three years, but players definitely have a duty of care to know where the umpire is at all times.

"You should know where the umpire was.

"He was in bright orange, so you can't miss him."

Rendell said Koschitzke was disappointed but had received a very fair hearing.

"Obviously it's a pretty forceful blow to the back of the umpire's head so we feel sorry for him, but he's OK, and Kosi will be OK in a little bit of time," he said.

Koschitzke is one of the Saints' most talented and influential players, but has endured a shocking run with injury since he made his debut in 2001.

His forgettable 2006 also included fainting on live national television.

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