Clarisse McClellan is indirectly characterized as outgoing in Fahrenheit 451. For example, in the beginning of the book when Clarisse first meets Montag, she speaks to him as if she's known him her life. The reader can tell that Clarisse is far from shy by the way she acts toward Montag. The two of them carry on a conversation, and walk home together. This is indirect characterization because the author does not come straight out and say Clarisse is outgoing, but the reader can infer from the events that occur throughout the story.
Clarisse McClellan is directly characterized as crazy in Fahrenheit 451. One example of this is when Clarisse is talking to Montag for the first time and is explaining herself. "I'm seventeen and I'm crazy," Clarisse says. This is an example of direct characterization because the reader can find directly where these words were spoken in the story. The reader does not have to infer anything or look for any further information.