I'm not sure why people have such trouble seeing why this hit Mincheol so hard. It was very clear the whole time leading up to his accident that he was already burning himself out, and as if that wasn't enough Haneul wasn't even at his school to cheer him up. Since he's not as sociable this left him completely alone, at a time where he was already self-deprecatingly ruminating. He clung to baseball hoping it would give him confidence to stand beside Haneul but in the end all his efforts and pain were for nothing. That's already devastating, let along the rehabilitation for the injury, and Haneul falling off the stairs and being hospitalised was just the cherry on a very stacked depression cake.