you are not in a hurry but somebody else will come who will be in a hurry.
这句话中的who will be in a hurry 是个定语从句,是用来修饰somebody else的,本来是应该接在somebody else的后面。这句话正常的语序其实是这样的:you are not in a hurry but somebody else who will be in a hurry will come.它只是为了避免句子头重脚轻才这样放的。