Ball tracking ruled Mitch Marsh lbw but Aussie commentators say it's missing leg stump.

Former Test star Mitchell Johnson has labelled the decision review system a failure following Mitch Marsh's controversial dismissal during the first cricket Test against South Africa.

Marsh was originally given not out when he was struck low on the pads by a swinging Kagiso Rabada delivery on Monday.

But the decision was over-turned when the ball-tracking technology used by DRS predicted the ball would have clipped leg stump.

Paul Kane "Just saw Mitch Marsh's lbw.... what a crock of $&@! DRS system = Failure," Mitchell Johnson wrote on Twitter.

Most Australian observers were stunned, thinking the ball was angling well down leg side.

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"Just saw Mitch Marsh's lbw.... what a crock of $&@! DRS system = Failure," Johnson wrote on Twitter.

MARK KOLBE/GETTY IMAGES "I was certain that was missing the stumps," Michael Clarke said while commentating on Channel Nine.

Former Test skippers Michael Clarke and Mark Taylor shared similar sentiments.

"I was certain that was missing the stumps," Clarke said while commentating on Channel 9.

"When you look at that replay, I thought it was definitely swinging too far and missing the leg stump. He'll be really disappointed with that.

Mitchell Marsh was originally given not out but the ball-tracking technology used by DRS predicted the ball would have clipped leg stump.

"What I don't agree with is the line of the delivery once the ball hits him on the toe.

"I believe the line of that delivery is going down and missing leg stump."

Taylor said Marsh (26) was unlucky to be given out.

The DRS also came under fire in Australia's first innings when Steve Smith was given out lbw despite charging well down the pitch to play spinner Keshav Maharaj.

Smith appealed the decision but the DRS showed the ball clipping leg stump.