同位语从句与定语从句形相似而质不同，常有以下几个区分点：

1.同位语从句前面均为抽象意义的同位名词，如fact, idea, view, thought, order, suggestion, news, truth, hope, promise, answer, belief等等；而定语从句的先行词却无此限制。

2.同位语从句解释同位名词的具体内容，而定语从句则是对先行词进行限制或描绘修饰。比较：

The news that they won the football game is exciting. 他们赢得了足球比赛这个消息令人兴奋。(同位语从句，消息的内容是“他们赢得了足球比赛”)

The news that he told me was not true. 他告诉我的消息并不真实。(定语从句，限定消息是“他告诉我的”)

3.that引导同位语从句时，起连词的作用，无实际意义，不充当句子成分，一般不省略（尽管间或有人省略）；that 作为关系代词，引导定语从句时要充当从句中的成分，作宾语时常省略；比较:

She received the message that he would come by air. 她收到了他将乘飞机来的消息。(同位语从句，that无实际意义且不省略)

The message (that) she received made her very surprised. 她接到的消息令她感到十分意外。（定语从句，that在从句中作received的宾语且可以省略）

4.同位语从句还可用what, when, how, whether等连词引导，而定语从句则不能。

I have no idea when he will come back. 我不知道他什么时候回来。(同位语从句)

The problem whether he will be fired is under discussion. 他是否会被开除这一问题正在讨论。(同位语从句)

Ozil agreed a long-term contract at the Emirates Stadium on Thursday after speculation he could leave for free at the end of the season. 

解答如下:

he could leave for free 是定语从句修饰 speculation .如果把 he could leave for free 去掉，after speculation at the end of the season 这句话在句子中是什么结构属于介词after +名词speculation,构成介词短语在句中作状语