Hermione would usually be very worried and immediately start looking for ways to heal him. She might use her knowledge of magic to find the right spells or potions to treat his injuries.
Ron would be quite protective. He might get angry at the person or thing that caused Harry to get hurt, whether it was a Bludger or an opposing player. He would also stay by Harry's side, offering moral support.
His friends would be extremely worried. They might immediately drop whatever they are doing to rush to his side. For instance, Thomas would be right there, trying to assess the situation and figure out how to help. He would be filled with a sense of urgency and determination to get Minho the care he needs.
If his friends continue to ignore him, Harry could become sad and withdrawn himself. He might start to isolate more, spending time alone in places like the Forbidden Forest or an empty classroom. He might also lose his confidence in himself, thinking that he is not worthy of their friendship. In his loneliness, he could focus more on his studies or some solitary magical pursuits, trying to distract himself from the pain of being ignored.
Simon might be in a bit of a panic. Since he's her friend and also not as used to the dangerous situations as the other Shadowhunters. He'd try to do whatever he can to help, like getting help from more experienced Shadowhunters or trying to comfort Clary while she's in pain.
His friends would most likely rally around him. Kiba might use his dog Akamaru to scout the area and make sure there are no other immediate threats. Hinata would be really worried and would try to use her Byakugan to see if there are any hidden enemies or if Naruto has any internal injuries. Choji would offer some of his food to Naruto to give him strength, as his clan's food can have special effects on a ninja's body.
He might initially be confused. Harry could keep trying to engage with his friends as usual, not really understanding why they are being cold towards him.
Hermione would immediately start researching ways to heal him. She'd pour over ancient books and consult with the most knowledgeable wizards to find a cure or at least a way to ease his pain.
Raph usually gets really angry. He blames himself for not being there to protect Leo or he gets mad at the enemy who hurt Leo. He'll be the first to want revenge and will be very protective of Leo while he's injured.
The other characters' reactions can vary. Pixal, if she's around, would use her technological knowledge to see if there are any internal damages to Jay, especially if it's related to his electrical components. The villagers of Ninjago might also show their support. They could bring food or offer shelter for Jay to recover. The reaction of the villains would depend on the situation. Some might see it as an opportunity to finish Jay off, while others might be impressed by his courage in getting hurt while fighting them.
Timmy's friends' reactions can vary. Cosmo might accidentally make the situation worse by using the wrong spell in his haste to help Timmy. Wanda would be more level - headed and try to correct Cosmo's mistakes. Chester and AJ would be really concerned and would try to comfort Timmy. They might hold his hand or tell him that he'll be okay. In some fanfictions, if Timmy is in a coma or seriously injured, his friends would be constantly by his side, waiting for him to wake up and doing whatever they can to speed up his recovery.
Kagome usually gets very worried. She'll immediately try to use her spiritual powers to heal him if she can. If not, she'll search for herbs or other ways to help. Miroku would likely offer his support in a more practical way, like finding a safe place for Inuyasha to rest. Sango might be on guard, making sure that no more enemies take advantage of Inuyasha's weakened state.