A hedgehog rolls itself into a ball when attacked.

刺猬一受到攻击就蜷缩成一团。

《新英汉大辞典》

Your instinct when attacked is to defend yourself.

你受到攻击时的本能是保护自己。

youdao

Those people liked Lawton in part because he hit back when attacked.

这些人喜欢劳顿的部分原因是在他遭到攻击时，他会反击。

youdao

Researcher Reed Johnson, now at the University of Nebraska-Lincoln, says the study suggests that the damaged proteins are unable to respond effectively when attacked.

VOA: special.2009.09.15

It was said that when Horus was a child, he was attacked by Seth, the demon of evil.

VOA: special.2009.03.22

Stress results when something causes your body to act as if it were being attacked.

VOA: special.2009.03.24

Many members of Congress spend weekends holding open events, as Ms. Giffords was doing when attacked.

WSJ: Shooting Spurs Calls for Security, Civility

In the Springfield Road area three police officers were injured when attacked while separating rival factions involved in clashes.

BBC: News Online

This style of warfare also makes it more difficult for the army to strike at Unita's bases, and easier for the rebels to adapt and regroup when attacked.

BBC: Analysis: Unita's changing tactics