Norton calls Lorraine a screech owl in chapter 9 of Paul Zindel's book The Pigman. That is about halfway through the book, and by that time John and Lorraine have become fairly good friends. They have become good friends with each other and with The Pigman himself. What started off as a prank call to Mr. Pignati wound up starting off an odd, but fruitful, relationship between the three characters. The best answer that I can give you for why exactly John defends Lorraine from Norton, is that John is friends with Lorraine and respects her. He doesn't like it when somebody bad mouths her. John especially doesn't tolerate that kind of talk from Norton. John doesn't really care much for Norton.
"He is so low on the scale of human evolution he belongs back in the age of the Cro-Magnon man."
In fact, John's thoughts about Norton are so low that John ends the chapter by thinking the following line.
That was the Pigman, and I knew I’d kill Norton if he tried to hurt the old man.