But I need to sit down so what happens if I can't move and they are standing in front of me?
Ask these people to sit down, and explain why you cannot stand up due a condition you have, and surely any decent Fulham supporter should adhere to your request. Or at the very least help you to be in a position to view the action. You have paid for your ticket so you are entitled to watch the match without any restrictions.
Your only other course of action is to alert the Stewards, that’s what they are there for.
Nobody can blame you as the selfish people who are preventing you from watching the match have orchestrated this situation, they are responsible for their lack of civility.