Perhaps another demigod who is jealous of her skills and intelligence. This rival demigod could set up a dangerous situation for her during a competition or a mission. For example, they could tamper with some equipment she needs to use, causing her to get injured when it fails.
It could be an enemy from the underworld. Maybe a powerful demon or a vengeful spirit that has a grudge against her. They might use their dark powers to harm her, like sending a bolt of dark energy her way.
Maybe it's a human who has somehow discovered the world of demigods and is afraid of their existence. They shoot Annabeth out of fear and misunderstanding. Another option is that it's a rogue demigod who has gone bad and is working against their own kind. This character could have a personal grudge against Annabeth specifically, perhaps because of her intelligence and leadership skills which they envy.
It could be a rival from another house. For example, a jealous Slytherin who wants to take Ginny out of the Quidditch game. They might use some underhanded tactics to make her broom malfunction and cause her to get hurt.
Maybe it's a jealous acquaintance. If Kagami is really good at something, like she's a star in a particular activity, someone who is jealous of her success might set up a situation where she gets hurt. For instance, they could tamper with her equipment in a way that causes her to have an accident.
In some cases, it could be herself. Maybe she pushed herself too hard in her work or training, and her body or mind couldn't take it anymore. This self - inflicted harm could be a key part of the fanfiction's plot, as she then has to deal with the consequences and learn from her over - zealousness.
It could be an over - enthusiastic fan at an iCarly event. The fan might be so excited to meet Carly that they accidentally knock her down while rushing towards her.
His siblings could be responsible. They are always getting into crazy situations together, and maybe one of their pranks or games goes too far and accidentally hurts Lincoln.
In this fanfiction, it might be due to the extreme weather conditions. A sudden and powerful blizzard could cause an avalanche, and Everest, being in the wrong place at the wrong time, gets caught in it and is hurt. She might be trying to help some animals find shelter when the avalanche hits, and her selfless act could be what leads to her getting injured.
Another possibility is a jealous student at Hogwarts. There are always students who might be envious of Hermione's academic achievements. They could set up a prank or a trap that goes wrong and ends up hurting her. For example, a student who is tired of Hermione always getting the top grades in Potions might tamper with her cauldron during a class experiment, resulting in an explosion that hurts her.
It could be a new, inexperienced doctor. Maybe they make a mistake during a surgery that Meredith is involved in, accidentally causing her harm. For example, they might misread a vital sign or use the wrong instrument.
It could be a rival assassin. They might see Kassandra as a threat to their own reputation or contracts.