I voted for "It came naturally," cause I think that's the most relative answer, although all of those options probably did contribute to Simba's fighting skills overall. Lion cubs learn a lot of the skills they need in later life when they are young, through play and observation, and while Simba didn't exactly have the easiest cub-hood, we still know he learned some things from Muffy and by playing with Nala, but probably not as much as he would have if things didn't go the way they did. While I think he might have learned a thing or two about fighting while he spent his time in the jungle (as shown during the scene when he's trying to protect Pumbaa and Timon from getting eaten by Nala when they first reunite), I doubt he really learned much from them in regards to fighting at all. I think brute strength did play a part in his victory over Scar but like I stated, I think the choice of it coming naturally is best suited for this poll. Like Mike stated, fighting is sort of a natural instinct for lions and regardless whether one has been taught how to fight or not, if they feel threatened or are pushed to the point where fighting is their only means of survival, anyone would be able to dish out a punch or two no matter how skilled they may have been.

I think Simba was going off pure hatred towards Scar by that point in the movie and after seeing his mother being abused, knowing that Scar killed his father and having his own uncle being on the brink of killing him, that would trigger his natural defense mechognisms as a lion. ^^ Same would probably go for any creature actually, but yeah, that's just my two cents.
