Even though the prompt you ask about is vague ("uncommon" in what way?) you still have numerous angles you could use to write a thesis and essay for Shakespeare's Macbeth.
Of course, Macbeth is the actual protagonist in the play, and Macduff is the antagonist. But if you have to, you could make a case for the witches being protagonists. After all, they apparently set out with a goal in mind: to create chaos in Scotland, to destroy a righteous king and replace him with a dictator, to bring about the destruction of Macbeth. They put their plan into effect, take the necessary steps to accomplish it, and are successful. It may be uncommon to think of the witches in this way, but the fact is that they win, they are successful in achieving what they set out to achieve.
Other possibilities might be:
- Banquo as antagonist (he suspects Macbeth of treachery, yells for his son to flee thereby ensuring that Macbeth will fail to create a dynasty with his own heirs, and appears as a ghost which makes Macbeth suffer a "fit" in front of his Thanes)
- Lady Macbeth as protagonist (she devises the plan to assassinate Duncan and convinces Macbeth to go through with it, and she suffers a fall just like a protagonist should)
The above are a bit of a stretch, but they are possibilities for you to use.