Recent violence has been attributed to a group of foreign fighters，referred to by locals as the Ten Rings.
【翻译】最近的暴力事件被归咎于一群外国士兵，被当地人称为“Ten Rings”。

我把句子变成主动语态；然后把过去分词短语referred to by locals as the Ten Rings，变成定语从句，你就知道是怎么回事了：

People have attibuted recent violence to a group of foreign fighters，which is referred to by locals as the Ten Rings.

1. attribute...to...     被动语态是...?

2. be referred to as...     主动语态是....?

这两个词组，交给网友查词典。