This is the barebones of a idea I had, please leave any suggestions in the comments for how I should improve it or any extra things I should add.
----------------------------------------------------------
After Bran falls from the tower, Ned reluctantly brings jon with him instead as rickard is too young and he needs a son in kings landing, plus he knows jon would give his life for his daughters
Ned Stark demands trial by combat/7, ned is injured badly, leg, can barely walk, his men are all dead, Sansa is under royal control, Arya is somewhere in the city, Barristan wants to but cannot, seeing no one stepping forward, a 15 year old jon steps forward to fight for his 'father', he is up against Ser Jaime 'Kingslayer' 'Golden Lion' Lannister, Jon wields Ice and Armour dark as night forged by Tobbho Mott, and Joffrey and Cersei make it a grand event by allowing the small folk to witness it in the arena/tourney grounds, whatever Lords are close attend, Jon fights with fury, his helm thrown off his head and taking a cut over his left eye and down the right side of his face, before cutting Jaime's sword in half, Jaime is thrown another sword and cuts across Jon's chest leaving a mark across his armour, jon follows up by hammering Jaimes defense vigorously, until he is disarmed, the person assigned to be his 'squire' of sorts, is a random Goldcloak, tosses him a warhammer far too heavy, and as Jaime goes for the killing blow, in a fit of rage and despair, jon muster the strength to swing the hammer at Jaime, breaking his right arm, then falling over to the ground, quickly stumbling back as jaime roars in pain, jon makes a jab about the Roaring lion and how he lives up to his houses words, before jaime tries to swing at his with his left, jon dodges but drops the warhammer, and runs to grab ice, before beating jaime squarely with superior skills, stabbing through his armour before Jon stabs his through, and Cersei demands a stop to the trial and sends her guards to stop him, Tywin sees the state of his 'heir' and sends his own men to save Jaime, Jon and Ned are locked away in the black cells.
Option 1
Ned is executed still, but jon breaks out grabs ice kills the executioner in the dungeons, and cuts his way through the castle, finding joffrey with sansa, Cersei and various other young ladies and servants, Jon rushes forward in fury and stars Joffrey through, then cutting off his head, then stabbing cersei before grabbing Sansa and the crown, and running, down the servants paths jon knows because that was where his rooms were, courtesy of cersei and her hatred of bastards, as her fear of Robert legitimising his own bastards threatened he children and her ambitions, before escaping into the city, down into the docks and onto a bravossi ship, before remembering Arya and running off of it, leaving Sansa, and into the city finding Arya crying, filthy, and curled upon a gutter, grabbing her and dragging her back the ship, hiding in the small cabin with Sansa and Arya
Option 2
Suggestions?