In Act I, scene 2 "Macbeth," when the king sights a bloodied solder in the camp near Forres, he asks Malcolm, his son, if the man can give a report of the battle.  Malcom replies that this brave and "hardy soldier fought/Gainst my captivity." (I,ii,4-5)  The man has been engaged against Macdonwald and has saved King Duncan's son from harm.  This captain explains what has happened against the lightly armed Irish foot soldiers and the heavily armed ones, as well:  the "kerns and gallowglasses" (I,ii,13).

In the midst of this engagement in which "fortune" seemed to favor Macdonwald, "brave Macbeth" entered, "disdaining [showing contempt for] fortune with his "brandished sword" (I,ii,17), and executed men until he reached Macdonwald, "the slave,"(I,ii,20) of fortune.  Peremptorily, Macbeth without so much as a word, brutally slay the man, "unseamed him from the nave to th'chops," cutting him open; then he took off the man's head and impaled it upon the "battlements" [the walls of battle].

Then, the King of Norway arrived and began a fresh assault.  But, when the king asks if Macbeth and Banquo were not worried when this happened, the captain replies that they were only as concerned as an eagle would be by the attack of a sparrow, or a lion being confronted by a hare (I,ii,.35).  They simply

redoubled strokes upon the foe./Except they meant to bathe in reeking wounds,/Or memorize another Golgotha (I,ii,38-40)

With this recounting of the battles and the actions of Macbeth, the captain clearly indicates the brutality with which Macbeth fights, not only slaying, but  eviscerating and beheading his enemy; he later makes a bloodbath of the battlefield, so much so that the captain compares it to where Christ was crucified.  But, to all this information, King Duncan remarks at how brave Macbeth is, thus, foreshadowing that his poor judgment will leave him vulnerable to Macbeth later on.