The reason it's complicated is because of his actual role on the team during his middle school years. Sure, he was good physically, but his actual strength was his analysis of his opponents. During a match, he could identify holes in their opponent's defense or specific offensive tendencies, and he would direct his teammates mid-match to compensate and exploit. It's how their team rose so quickly and became a dark horse contender to win this major tournament. But the problem is that they got overreliant on his input, so when he failed to show up for the opening game of the tournament - a game that he'd promised he'd attend the day before, but was prevented from doing so as previously mentioned - the team basically collapsed on the field, and his friend injured himself by overexerting and trying to make up the difference. The other teammates were so shook up by the colossal pounding they took and the apparent betrayal of one of their team leaders that they lost faith in the team itself and quit en masse.
Yes, he's going extremely heavy with the self blame, but a lot of people will do that if they can't fulfill a promise they made, even if it's not their fault it couldn't be fulfilled. He has reasons for not speaking up about his failure to attend, but public opinion can be hard to sway when you're already accused, and his recently-acquired new guardians - who had physically prevented him from going (he was literally locked in his room until he could break out) - have a lot more clout than a middle school aged boy. So in the end, he gave up on the sport, fully embraced the public label of "villain" he had received, and decided this was his means of atonement for cutting short the careers of at least some of his teammates. I won't say he's not taking his martyrdom too far; hell, his teacher has said as much as early as chapter 1. But stubborn people with set convictions like this exist both in fiction and reality, so it's not as though his actions are entirely unrealistic, especially given Japanese society.
It should also be mentioned that no one has really discussed his family situation just yet, which is a whole other can of worms, even if it did contribute to the whole soccer issue. That issue will actually be touched upon first, believe it or not, before the entire sports thing gets explained in the story.
and in here, Charlotte looks straight-up jealous of Shinonome 
