Ulfric challenging a young man with no actual combat experience, while he is a highly season war veteran with the ability to throw people across the room with three simple words is kind of cheap.
So if Torygg had been older and more experienced in combat and also trained in the Thu'um, then Ulfric's challenge and Torygg's death would've been perfectly acceptable? Because if not, then the issue of Torygg's age, ability and experience is irrelevant. It's just a convenient way distract people from the issue of whether or not the duel was legal in the first place.
If the duel was legal, then Torygg's age and inexperience are immaterial. He was the High King, the High King can be challenged, it's an occupational hazard that one agrees to when one takes the throne. If the challenge is accepted and the duel takes place then neither winner is a murderer regardless of the outcome.
if it was illegal, then nobody's age and experience are relevant because both men agreed to participate in an unlawful act which resulted in the death of one at the hands of the other. Regardless of the outcome, whoever survives is guilty.
Torygg's age and inexperience may have made him an easier man to beat, but it was his position as High King (and his apparent political sympathies) that put the target on his back in the first place. IMO had he been an older and more experienced man the target would have been there just the same.
And unless you're willing to accept the idea that Torygg would've been charged with murder had he won, then any complaints about the illegality of the duel are meaningless. If Torygg could've killed Ulfric somehow in the course of violating the laws of the land and still walked away a free man, then the same must apply to Ulfric when he wins. Otherwise the "law" is either being invented on the spot or selectively enforced simply because those who are in a position to invent and enforce it don't like the way things turned out. And that really does nothing to help the Empire's case, lol.


