I can shed some light on this as I was sat by it!
Basically, at the start of the game a bloke and two ladies arrived to find some blokes (one chubby one in a blue shirt, and one scrawny, taller one) sitting in their seats. They kindly asked them to move and were aggressively told to fuck off. Stewards took ages to help; first a woman walked up to them an bottled it, and then another woman approached them and demanded to see their tickets.
A little scuffle ensued and the chubby lad pushed her in the face with his arm but, luckily for him, Sergio scored his first goal and of course everyone stood up. She went back to the waiting trio - who still hadn't been able to sit down - basically shrugging and giving up. At this point my brother went over and said to her that perhaps she could get these three up into Club Wembley as there were loads of spare seats and it would defuse the situation, but the steward just threw her arms up in the air. By now the two idiots had scarpered, but I think the steward wisely took the waiting trio up to Club Wembley or to some other seats.
Anyway, second half and the two are back, arguing with everyone around them. One lad behind them seemed to say something and the scrawny tall idiot squared up to him and his chubby mate got involved. Then came the threats and the pushing - all this going on where lots of young families, kids and old people were sitting. Stewards just sat and watch, despite people screaming at them to intervene. It was pathetic.
Eventually three stewards, young lads, came to drag them out. One of them got punched a few times by the chubby one but kept his cool. People were falling over seats, kids crying etc., before they were dragged away - which I guess is the apart you saw. I think as they got dragged away other fans gave them grief and they just wanted to fight everybody.
In the last three times I've been to Wembley - Arsenal Community Shield, last LC Final and yesterday - I've seen blues fighting each other. Powder certainly behind it judging by the way they all acted. I missed both goals yesterday because of the commotion, and it's horrible to see women and kids getting upset. The worst part was how the stewards did nothing to get them out of the seats the first time around, and then just stood idly by for at least ten minutes whilst the fight was breaking out. As we walked out at the end my brother said to a copper words to the effect of "Where the fuck were you?" and he said that they aren't allowed into seated areas, only stewards.