they met in the castle and bam the battle began !
MacDuff kills Macbeth.
Macduff kills Macbeth. It says so in the script.
If you are referring to Shakespeare's classic Macbeth, it's because Macduff hates Macbeth. Remember, Macbeth turns evil because of hunger for power. Macbeth killed Macduff's wife and children because Macduff knew Macbeth killed Duncan. He wanted to kill Macduff, but Macduff was gone. Macbeth killed Macduff's family because he felt they were in his way and stopping him from achieving his goals.
Ross informs Macduff that Macduff's family has been murdered on the orders of Macbeth.
Macduff enters the battle holding Macbeth's head, triumphant in victory. He declares to all that Macbeth is dead and that the rightful heir, Malcolm, will now be king.
Macbeth is killed in battle by Macduff. Macduff reveals that he was not "born of woman" in a traditional manner, fulfilling the witches' prophecy that only a man not born of woman can defeat Macbeth. Malcolm, the rightful heir, is then crowned king.
After he crosses the brink of insanity, Macduff and Malcolm lead forces to retake the throne. In a battle, Macduff kills Macbeth and delivers his head to the new king, Malcolm, who then begins the Tudor-esque age in Scotland (making the Thanes into Earls)
In Shakespeare's play "Macbeth," Dunsinane Hill is where the final battle takes place between Macbeth's forces and those of Malcolm and Macduff. Macbeth is ultimately defeated by Macduff, fulfilling the witches' prophecy.
Macduff wants to go to war against Macbeth because he believes Macbeth is a tyrant who has unlawfully seized the throne and is responsible for the murder of King Duncan. Macduff is also motivated by a sense of duty to restore order and justice to Scotland.
They are not friendly from the very start. When Macbeth is to be crowned, Macduff decides to go home to Fife rather than attend this important event. That's not a very polite thing to do to a king.
Lady MacDuff and her children are killed in Act 4 of "Macbeth". Macbeth hires assassins to kill the MacDuff family because he fears MacDuff is plotting against him..
Macduff is the character who ultimately escapes death in Macbeth. He was not "of woman born" as foretold by the witches, and is able to defeat Macbeth in the final battle.