Do you believe the narrator of "A & P" is a static or a dynamic character?
Let me explain what dynamic and static characters look like and give you a couple examples of each. then you'll be able to answer this question for yourself.
A dynamic character undergoes some kind of significant change in the course of the story. It may be what we call a change of heart, or a moral change. This change does not include a change in physical appearance but in personality, attitude, morality, and the like. An example is Ebenezer Scrooge, who is a mean old miser at the beginning of the story and a kind, generous, loving man at the end. Another example is Edmund in The Chronicles of Narnia.
A static character remains the same at the end of the story as he or she was at the beginning of the story. No matter what happens to these characters, their personalities and attitudes don't change at all. The fact that they don't undergo any kind of change is not necessarily a bad thing. It could be that there is no lesson they need to learn or change to make. In A Christmas Carol, Bob Cratchit is a static character. He remains the same loyal employee to Scrooge from beginning to end.
Now, which kind of character do you think Sammy is?
I believe Sammy is a dynamic character, meaning one who changes in some way at some point in the story. Sammy is, in many ways, a typical teenage boy with a part-time job he doesn't enjoy and a penchant for attractive young girls. He wants to be the "hero" to the young girls by "sticking up" for them when the grocery store owner is rather mean to them; however, Sammy fails to realize that even if he DOES defend the young girls, he is doing it for all of the wrong reasons. He isn't really doing it because he really wants to defend the girls; he is doing it because he wants the glory and recognition. Sammy makes his change at the end of the story when he has an epiphany, a moment of enlightenment. He realizes once he's quit his job that life is a lot more difficult and complicated than he ever realized and that it will continue to be that way.