Only after he had spoken out the word did he realize he had

状语是用于说明地点、时间、原因、目的、结果、条件、方向、程度、方式和伴随状况等的句子成分.
可以做状语的有：1、副词；2、分词或分词短语；3、不定式；4、介词短语；5、从句.
Only after he had spoken out the word did he realize he had made a big mistake.该句中Only放句首句子实行部分倒装,倒装的部位就是状语成分.因此,该句的状语成分在“did he realize he had made a big mistake”,原形为“he realized he had made a big mistake"