Why didn't Cedric duel with Wormtail?

Question

When Harry and Cedric were transported to the graveyard by the portkey, they saw Wormtail coming to them carrying something. Harry's forehead starting aching wildly so he was unable to duel but Cedric was up and could have fought. But it seems from the passage that it was a complete surrender.

From far away, above his head, he heard a high, cold voice say, "Kill the spare."

A swishing noise and a second voice, which screeched the words to the night: "Avada Kedavra!"

A blast of green light blazed through Harry's eyelids, and he heard something heavy fall to the ground beside him; the pain in his scar reached such a pitch that he retched, and then it diminished; terrified of what he was about to see, he opened his stinging eyes.

Cedric was lying spread-eagled on the ground beside him. He was dead.

My question is, Cedric didn't know that there was Voldemort in the rags Wormtail was carrying. He was just attacked by a stranger and he should have fought back. But he didn't. I know he was still a student and Wormtail was a fully grown wizard but few minutes later his junior in school was dueling with the most feared dark wizard. Cedric wasn't a coward for sure. So why didn't he duel?

Answer 1

It happened too fast for Cedric or Harry to react. They didn't know what they were doing. As your quote suggests, it happens in a blink; they didn't know that something that drastic was going to happen so fast. That said, they were ready, supposedly for a fight.

"I dunno," said Cedric. He sounded slightly nervous. "Wands out, d'you reckon?"

"Yeah," said Harry, glad that Cedric had made the suggestion rather than him. They pulled out their wands. Harry kept looking around him. He had, yet again, the strange feeling that they were being watched.

"Someone's coming," he said suddenly.

Then they lowered their guard a bit when there wasn't an immediate attack:

Harry lowered his wand slightly and glanced sideways at Cedric. Cedric shot him a quizzical look. They both turned back to watch the approaching figure.

Furthermore, Harry was rendered helpless, which would've distracted Cedric.

And then, without warning, Harry's scar exploded with pain. It was agony such as he had never felt in all his life; his wand slipped from his fingers as he put his hands over his face; his knees buckled; he was on the ground and he could see nothing at all; his head was about to split open.

You have to remember there is also nothing that can be done about The Killing Curse. Yes, he should've engaged before then but he's just a seventeen year-old and doesn't know that someone with murderous intent is walking up on them until it is too late.