"When Ulfric Stormcloak, with savage Shout, sent me here, my only regret was fair Elisif, left forlorn and weeping."

"I faced him fearlessly - my fate inescapable, yet my honor unstained - can Ulfric say the same?"

So, in my current playthrough of Skyrim I remember going to Sovngarde and speaking to the expired High King, and I had an idea. I wonder, knowing that he was no match for Ulfric, allowed himself to be killed without a fight, in order to stain Ulfric's name further?

I remember Proventus saying when you deliver Ulfric's axe to Balgruuf, that Ulfric simply walked up to and murdered Torygg. Of course, I'm not sure why Proventus would be in Solitude, but I thought it interesting in the context of the rest of my idea.

It very well might be a crackpot idea, but I thought I'd see what you guys think of it.

Unlikely, He IS a nord, Torygg probably did it because of honor.

If Torygg had done as you describe, for the reason you ascribe to him, he would not be in Sovngarde. If he suicided by not fighting, in order to diminish Ulfric's honour, then his own honour would have been stained. Therefore he fought, because honour (wrapped up in the challenge) demanded it.

I have to wonder if the High King accepted, knowing full well he would lose... But did so in the hopes that his death would shake things up within the empire and Skyrim. Sort of his way of saying "Look, you stood by long enough and let the thalmor pretty much wash over Skyrim doing as they will... now the people have risen up and revolted, I their king is now dead. DO YOU GUYS GET THE POINT YET? THIS IS NOT RIGHT!"

That's just my theory. The duel in accordance to the laws of the nords was fair. So was Ulfric using his voice. Think about it, the challenger is not doing so to be fair. He is doing so to make a point, a statement. That the empire is weak and so are the puppets they have on the throne. Had the high king known shouts I am sure he would have surely used them against Ulfric in order to show he was strong enough to lead. People often forget that...

Personally were I to be challenged by Ulfric in a duel, hopefully I could kick him hard in the balls first so his shout didn't come out right... Come on... anything to win right?

No, because when one goes to Sovngarde they leave their hatred, anger, and all other past pettiness behind them. http://mkerala.com/u/di/PDJW/2014-04-12_00077.jpg if you speak to him after having completed http://mkerala.com/u/di/R2KS/2014-04-12_00078.jpg. Basically, Torygg spoke true.

Does it matter? Ulfric used a shout on a man you had no real warrior training, no training whatsoever in the thu'um or how to defend against it. Legal or not, or whatever Torygg's reasons for it, Ulfric stained his own honor by winning the way he did.