Without the context of the sentence, it is difficult to determine why the word "again" might be underlined. However, here are a few possible reasons:
The word "again" may be underlined to indicate that it is a word that is commonly misspelled or used incorrectly. In this case, the writer may be indicating that the word should be double-checked for accuracy or that it needs to be used in the correct context.
The word "again" may be underlined to indicate that it is a word that the writer wants to emphasize or draw attention to. In this case, the underlining may be used for emphasis or to make the word stand out from the surrounding text.
The word "again" may be underlined as part of a proofreading or editing process. In this case, the underlining may be used to indicate that the word needs to be revised or removed from the sentence.