If Thrall continues to speak as he does the position of the Burning Blade within the Horde will be irreparably damaged. Your father will react as he's accustomed to, giving in to his impulses of pride and paranoia and the Horde will lose its most reliable source of expertise on demonic matters with the warlocks going their own way and falling to darkness.
But you can stop it.
"If you've ever trusted me do so now." you say, looking at your father.
He's almost crouched as if expecting an attack, claws ready, but then the statement shakes him out of his trance and his head snaps to you, "What-"
"Warchief!" you roar up at the dais.
The interruption is unexpected. Thrall's choice of arena and his effort to set the encounter up should have prevented such an attack but you lift your head and meet his eyes.
The crowd dies down swiftly as Thrall cuts himself off mid-sentence, staring at you in confusion.
"If anyone is responsible for this affair, for the march of Forneus and the Battle of Dreadmist it is me! I gave the orders, I had command."
You see Thrall's eyes flit to someone in the crowd, then back to you but before he can recover you continue.
"You speak of the Fel as corruption, a baleful influence on the Horde. Once perhaps, once when proud chieftains drank Mannoroth's blood, each more eager than the last to take the Legion's power. Now the Burning Blade use the Fel in defence of our people, as we did in the battle."
There's little space to gauge the crowd's reaction, you only really have time to try and draw attention to yourself rather than the clan.
"You claim that the Fel is the cause of our misery, yet I am a shaman. I went to Dreadmist to better connect with the Spirits, yet I also went under orders to oppose the Centaur of the Barrens. I ordered attacks on the Kolkar, I slew their leaders and then I found my position surrounded by thousands of enemies, far more than we had any knowledge of. I knew we had no hope of survival if we fought with honour so I ordered a delay. My warriors threw the Centaur back again and again, killing hundreds of them, and even then there was a thousand still left."
Thrall has some inkling of where you're going but clearly feels unable to confront you as you speak.
"I ordered the elders of our clan to summon a greater demon, one which could destroy the Centaur, even if we were destroyed also. Without such strength we'd have been lost, without our sacrifice and the deaths of my warriors the Kolkar would have swept across the Barrens, isolating our settlements and killing anyone they came across. I did as I did for the protection of our people, even if if meant the sacrifice of myself and my warriors."
"And yet the Centaur were provoked by the reckless use of the Fel against the Spirits!" Thrall replies, finding a response.
You pause. Thrall is right, his remarks confirmed, at least in part, but the Kolkar shaman who had thrown itself on your sword at the mountain. However you couldn't reply with counterpoints without weakening Thrall's position overall which you had no wish to do. The assembly has grown quiet, all that you can do is resituate the argument onto your own shoulders again, "I ordered this, I had command. I am no warlock, you know this well enough. I have not taken the Fel, yet I still gave the order, all that occurred is my responsibility, not the work of those who came after me."
"And you admit you abandoned your traditions for power? You abandoned your duty to the Spirits as a shaman?"
You frown at that. What is Thrall trying to do? Does he realise your strategy? Does he realise your attempts to counter his own rather than simply to mindlessly defend your clan? Or was he trying to get the debate back to his well-prepared ground of hearkening back to the Old Horde's actions?
"I am a warrior of the Burning Blade and a captain of the Horde. Those are my duties. Yes I understood the effect of this on my connection to the Spirits, but the Horde is greater than me. I acted as I did in accordance with my orders, if I have failed in this let the judgement and shame fall on me, not be diverted before this assembly to my clan…"
The last statement is a thrust at Thrall's strategy more directly than you've tried before, but clearly it strikes true, the Warchief's lips curling around his tusks. Your appeal and your piety have also been felt by the audience and you hear a low rumble run across the crowd as they speak among themselves.
One armoured figure in Thrall's party leans toward him. The Orc is old, grey-haired and speaks for a while, the Warchief inclining his head. Is this Saurfang? You've probably seen the Orc before but you certainly don't recall doing so, though you've been away for years in any case.
The conversation is quick but the noise from the crowd increases and then out of the corner of your eyes you see one figure leap to their feet.
"Honour!" the warrior cries, "Honour! For the Horde!"
Others take up the cry and though they aren't many another murmur goes through the crowd.
You look closer and see the figure is Sorek of the Blackrock, and those around him crying out too are Blackrock. You meet his eyes and he clashes gauntlet against his breastplate in salute. You have some friends here then it seems, more than you could have hoped for.
In the lull in conversation as Thrall still listens to Saurfang you look toward your father. His stance has shifted somewhat, less hostile but holding the same wary tension in his muscles. He looks between the Warchief and you, a strange expression on his face.
Finally the Warchief rises, taking up the Doomhammer, blue eyes looking sternly down at you, his black and brass armour shining in the sun, "Grok'mash of the Burning Blade, you claim responsibility for these events. Are you prepared to accept the consequences?"
"I am."
Thrall nods once, "Very well. As you say, you were the commander at Dreadmist, through your actions the Centaur advanced, and through your actions Forneus was summoned. Do you accept responsibility for this?" he asks again.
Neither were strictly true, but you had little choice, "I do."
"Through your failings and dereliction of duty to clan and people the Spirits have been roused to fury, the land broken and our city and people attacked, do you accept responsibility for these events?"
Again, you had no choice despite the inaccuracies Thrall was drawing you into, "I do."
Thrall raises his hammer above his head, "Then I pronounce your sentence. You served the Horde. No longer. You are exiled, cast out. You are no longer a part of this Horde, no longer one of our people. Go far from this place, you are unwelcome among us, your dishonour stains you like the blood on your hands. Go now to some faraway place and seek your future." his eyes flick from you to your father, "Let no Orc give you shelter or hospitality, let none even speak to you from this day forward. Let no person or clan give you aid lest they suffer under the burden of your sins. Go now, dishonoured and nameless, go now outcast, go now and leave us."
The doomful pronouncement might have sapped the strength of any warrior, leaving them downcast and sorrowful, but you look up at the Warchief and greet your exile with a smile.