If that rag is secure enough, it would snap his neck... if he used the thu'um. That's my guess.

And fail miserably.

Then what? The dragon would just proceed to kill Ulfric.

that would make great Comedy relief...

Ulfric: Fus!
Alduin: "Fus Ro Dah!"

and we suddenly see Ulfric and Tullius fly in opposite Directions

Exactly why it would be amazing.

Ok, I see now.

Has anybody heard Alduin's Thu'um when he's on top of the tower. You hear him say "Ba Qor" and "Ro Dah". He says it so menacing.

So that was the intention of the gag? i thought they just placed it there so they wouldnt have to hear on of his ''sons of skyrim'' boring speeches.

Two birds with one stone.

I'm well aware of that fact. My attempt at sarcasm failed

I think he chose not to shout out of fear of harming his men.

He's waiting for the shout cooldown.

Yeah, well the other guy in the duel never seems to mention getting stabbed to death after the voice "disabled him".

*shrugs* I still think Ulfric could be pretty powerful with the Voice at the level he is at.

Ulfric himself tells you he simply knocked down Torygg with his voice, then proceeded to stab him. Ask next time you visit him for the first time, he tell's you what actually happened.

If you think knowing two shouts makes him powerful? Then ok, I guess.

He was likely gagged, and even if he could still pronounce the dragonwords well enough to shout It likely wouldn't be beneficial to his well being to do so well gagged.

Now as for why he didn't shout during the ambush Trengs idea sounds likely.

Here's the logic: why would Ulfric deny a story that makes him even more badass?

No, he's got that annoying bug I sometimes get. He blocked or something, and even though his shout cooldown timer has finished, unless he blocks again he just can't shout. With his hands bound to his waist, no chance of that!

He's a modest chap, doesn't like bragging. Already escaped a brutal attack by Alduin that few others survived, no need to boast.

It's likely an enchanted rag of silence.

My idea exactly.

They gauged & bound him

Oh god, you stormcloak supporters are so cliche.

That's what Ulfric said. Most other people seemed to mention he shouted him apart. Ulfric never lets the facts obstruct his logic. Either way, getting rag-dolled before being stabbed while you lie on the ground isn't exactly honorable either.

Having watched the opening many times recently, the answer comes from Ralof while riding in the carriage: Ulfric told the Stormcloaks to stand down.

Ulfric beat down Forsworn by using his shout, i don't see how he get captured and gagged by the Imperials

Use your imagination. Maybe the Forsworn weren't as well prepared as the Imperials. Given the various accounts of how Ulfric eliminated Torygg, the Imperials wouldn't want to take any chances. Of course, it does pose another question - if the Imperials were that well prepared for Ulfric's shouting abilities, why didn't they just finish Ulfric off and refuse his surrender? Surely they would have used maximum force and not worried about taking Ulfric alive? Since the Imperials weren't bothering with parading Ulfric in front of the Emperor back in the Imperial City, 'public' execution in Helgen or not, they'd have Ulfric's remains to prove they defeated him. Mind you, they didn't expect a dragon to ruin everything.

If we talk to Alvor, he will say "..if you believe such story", so it means the Imperials didn't really believe the shouting things. The shout part is being exaggerated. Maybe Ulfric did use shout beating the Forsworn but not the main reason why the Forsworn are beaten. It just Nords are just being stronger than the Forsworn at that time. But still, the whole shouting thing being hyped just because that is the main thing of the game, being a Dragonborn can use shout, and so what we hear about shout are all exaggerated version.