This is a distinction that I find useful in my academic life, due to personal experience. You might find that you have different terms for this distinction, but I feel that it is an important one to make when characterizing a scholarly community.
What it comes down to is the role of shared practice vs. shared object of study. I consider “discipline” to refer to shared practice, while “field” describes the area of study of a particular object. Part of this is certainly due to the existing concepts of discipline and the metaphor of the field. Things that you work at, over and over again, take discipline. Discipline is a necessary quality for being trained in certain actions. And so in my mind, a “discipline” in an academic context refers to a training in a set of intellectual actions. On the other hand, the field is a spatial metaphor. I imagine a plain, empty but for a scarecrow in the middle. Perhaps this is the Middle Ages, and there is a band of archers making their way across to a group of armed farmers. Perhaps some mounted knights notice this and intervene. This little ecosystem of warriors is like an academic “field”: everyone is there, but they all have different ways of attacking the problem. A field is a space for common interest, not common training. For me, a field is defined by its object of study.
Some examples might help. One field that I find myself inside to some extent is Game(s) Studies. Judging solely by the name, we can assume that people in this field are interested in games. But there are so many possible ways to study games, ranging from ethnographic studies in virtual worlds to close readings of interfaces to AI work on programming companions. All of these fall under the umbrella, as long as the researcher can justify that they’re interested in games.
On the other hand, a field like English, while you might assume is similarly the field of the study of literature in English, is actually methodologically driven: a discipline. Scholars in English departments read “the canon,” they learn the basic disciplinary tasks of close reading and of writing essays. There’s more to it, of course, and it is true that every area of inquiry must communicate their findings somehow. But when it comes down to it, there is a way to “do English.” And that makes it a discipline.
Boundaries always shift, and things fall apart. What was once a field becomes a disciple as time goes on, thanks to the tightly networked nature of its members. What was a discipline becomes a field when its newcomers think “this is interesting but what if you look at it this way? Nothing is set in stone, and this is a good thing. But being able to identify whether the community to which you are speaking is a field or a discipline can help you (read: me) decide what kinds of justifications you need to make for your research and for your conclusions.