When David is saying goodbye to Mark, his mom, and the school nurse at the end, he takes one last shot at the basketball hoop. As he is doing this, a police officer can clearly be seen behind him down the street, likely guarding a barricade for the production crew.
After the Hulk and Jack's tussle, in the gym at Mark's school, you can clearly see the green make-up on front part, of his jacket sleeve.
Listen closely when David says regarding Mr. Hollinger, "He's also a child-beater, and that makes him very dangerous." Notice that the word "child" is over-dubbed. Mr. Banner's original line was, "He's also an egg beater, and that makes him very dangerous." The goof made several TV show outtakes and blooper reels over the years before the correction.