William Shakespeare's play, Macbeth, is considered a tragic play. Most of the characteristics of what deem a play tragic are well known to literary academics. That being said, a great site which lies out the characteristics is the Santa Ana College (linked below). Based upon this site's definition of tragic characteristics, Macbeth is considered a tragedy for the following reasons.
1. "Tragedy is concerned primarily with one person." The play follows the actions of one main character--Macbeth. While other characters are seen, everything revolves around Macbeth and his actions.
2. "The story is essentially one of exceptional suffering and calamity leading to the death of the hero." Macbeth suffers greatly. He murders his king (Duncan), loses his wife (Lady Macbeth), murders his best friend (Banquo), and, eventually, dies.
3. "The tragedy involves a person of high estate." Macbeth is a well known man among Duncan's followers. He is even regarded as high enough to be named as Duncan's heir.
4. "The tragic fate of the hero is often triggered by a tragic flaw (hamartia) in the hero’s character." Macbeth's tragic flaw is his overly ambitious nature. In the beginning, he was fine with allowing fate to take its course. After being pressured by his wife, his ambition grew. This ambition compounded as his power grew.
5. "Shakespeare often introduces abnormal conditions of the mind." Not only does Macbeth's mental instability become apparent (think his seeing of the dagger and of Banquo's ghost), Lady Macbeth goes insane as well.
6. "Supernatural elements are often introduced as well." In conjunction with number five, supernatural elements exist within the play. Macbeth sees a floating dagger and a ghost. Lady Macbeth sees a "damned spot" which will not come off of her hand.