Why is Macbeth angry at Macduff?
Macbeth's anger may stem from his great fear that Macduff will wrest power from him. While the play in no way suggests that Macbeth has ever been angry with Macduff, Macbeth's frantic actions on the battlefield in Act 5, Scene 10 attest to his descent to madness in his bid to hold on to his power.
It's no secret that fear often manifests itself in anger. Psychologists call this displaced aggression. Macbeth is afraid of the threat Macduff poses to him, so he lashes out in a seemingly illogical, rage-filled catharsis of sorts. In Act 4, Scene 1, the first apparition warns Macbeth to beware of Macduff. The second apparition, however, tells Macbeth that 'none of woman born/Shall harm Macbeth.' Macbeth thinks he is safe and has nothing to fear from Macduff. However, he thinks he will make doubly sure by killing Macduff anyway.
But yet I’ll make assurance double sure,And take a bond of fate. Thou shalt not live,That I may tell pale-hearted fear it lies,And sleep in spite of thunder.
...give to the edge o' the sword
His wife, his babes, and all unfortunate souls
That trace him in his line.
When Macbeth finally meets Macduff on the battlefield, he fights like a madman and refuses to give up.
I will not yield,To kiss the ground before young Malcolm’s feet,And to be baited with the rabble’s curse.Though Birnam Wood be come to Dunsinane,And thou opposed, being of no woman born,Yet I will try the last. Before my bodyI throw my warlike shield. Lay on, Macduff,And damned be him that first cries, “Hold, enough!”