Sydney Sixers opener Riki Wessels was struck by a vicious bouncer from Adelaide Strikers paceman Kane Richardson during the Big Bash League semi-final in front of a packed Adelaide Oval and he was confronted by the sight of the ball trapped between his protective facial grill and the peak of his helmet.

And in the 10th over he was struck for a second time on the helmet by a Shaun Tait screamer the ball before he was dismissed.

The 29-year-old son of former Australian and South African opener Kepler Wessels was playing a shot on the front foot when he appeared to be surprised by the bounce, pace and angle of Richardson's fifth ball of the fourth over.

He turned his head, as if to follow the line of the ball, and the television microphone picked up the sickening thud as the ball came to a sudden stop upon impact with his helmet.

While there was an extended break as Wessels composed himself, the batsman appeared unharmed by the delivery as he waited for a new helmet.

"That was a nasty delivery," said Channel 10 commentator Mark Waugh.

Adelaide Strikers batsman Brad Hodge, who was miked up for the host broadcaster, said the ball had "energy".

Wessels said he wasn't hurt by the bouncer.

The Sixers comfortably beat the Strikers to advance to the final. Read the full match report here.