South Australia skipper Travis Head has defended his decision to not allow Victoria a substitute player after Bushrangers wicketkeeper Sam Harper was hospitalised following a freak incident in Adelaide.

Harper was struck in the head by the bottom of Jake Lehmann's bat, the young keeper hit by the left-hander's follow through as he looked to pull a ball through the leg side.

Harper struck by bat in Sheffield Shield

The 20-year-old was taken to hospital for scans and ruled out for the remainder of the match, leaving the Vics with just 10 available players plus a substitute fielder who couldn't bat, bowl or keep.

Quick Single: Harper in hospital after blow to the head

The opposing captains discussed whether or not Victoria should be allowed a replacement player under the extenuating circumstances and, after discussing it with his teammates, Head refused.

While concussion substitutes are permitted in domestic one-day and T20 matches under Cricket Australia's new Concussion and Head Trauma Policy, the same rule does not apply to Sheffield Shield after the International Cricket Council announced in June they had rejected the new rule for first-class and international cricket.

In the event that a player is replaced, the match risks forfeiting first-class status.

Head defended his decision, but suggested the rule should be reviewed.

Report & Highlights: Vics romp to victory in Adelaide

"As a group, with no concussion rule (in place), we came to the decision that it wasn't going to be allowed and, rightly or wrongly, that is the way we went," Head said.

"It was definitely a tough decision, but we had a process of getting to that decision, and the group is 100 percent behind that.

"Going on this season with the amount of concussions, that (rule) is probably something that needs to be looked into."

Speaking on Saturday, Bushrangers coach Andrew McDonald said the fact his side wasn't allowed a replacement player was "unfortunate ... but that's ultimately South Australia's decision".

South Australia slipped to a 124-run defeat at Adelaide Oval on Sunday despite bowling out the Bushrangers on day one for a modest 204.

Highlights: Vics rip through Redbacks, seal win

The result puts the Bushrangers in the box seat at the top of the Sheffield Shield ladder.

The Redbacks' batting again let them down again on Sunday, out for 188, the third innings in a row they had failed to reach 200.

It was a second home defeat in little more than a week for the Redbacks who also lost unexpectedly against Western Australia last start.

Prior to the mid-season break, South Australia had won three of their five matches, holding a strong grip on second and within touching distance of the Bushrangers.

Head, who has spent the past month with the Australian team, was at a loss to adequately explain the dip in form.

"I have been away for a month and I chatted to a lot of the guys, and their thoughts and processes are the same," he said.

"Everyone has got their minds exactly as they did before Christmas, and it is just one of those things that we are not playing as well as we could be.

Replay all of South Australia's wickets

"In the last two games bowlers have been bowling quite well, but unfortunately we are not just getting the job done with the bat."

The Redbacks face Queensland next where a third straight loss could relegate South Australia to fourth.

Victoria commenced day three at 3-198 and extended their tally to 306, with Aaron Finch top-scoring with 71.

Chasing 313 for victory, the second-placed Redbacks were never in the hunt after being reduced to 3-15.

The only notable resistance came from Head on 47, wicketkeeper Alex Carey with 36 and some big-hitting from tailender Kane Richardson to get to 41.