How does Ender’s fight with Stilson in chapter 1 foreshadow his final battle against the buggers?

After school, several of the kids, including the lead bully, Stilson, taunt Ender. Soon they physically attack him, but Ender manages to manipulate Stilson into fighting him alone, playing off his pride and taunting, "it takes this many of you to fight one Third?" (Ender is the third child in the family, and Thirds are looked down upon.) When the others back off, Ender kicks Stilson, taking him by surprise, and drops him with the kick. Then, Ender walks up to him and kicks him several more times, making the point that he will win decisively so that no bullies will attack him again--the others will be far too afraid of Ender to try anything. After the fight, Ender sits down and cries until his bus comes, afraid that he is becoming vicious like Peter. Ender doesn't want to fight Stilson anymore than he wants to fight the Buggers. When Ender is forced to fight, he wins decisively. In both cases he regrets the violence that he inflicted.