One common scenario could be during a battle with a powerful enemy. For example, the Foot Clan might set up a complex trap and Leo, being the leader, might rush in to protect his brothers and get seriously injured. Another could be in a training accident. Maybe he's trying a new and difficult move and it goes wrong, resulting in an injury.
In some 'tmnt leo gets hurt fanfiction', Leo could be poisoned. Maybe an enemy uses a toxic weapon or a poisonous gas. He might initially try to hide his injury from his brothers because he doesn't want them to worry, but as the poison takes effect, his condition worsens and his brothers eventually find out.
Often, in this kind of fanfiction, Leo might get hurt while trying to save an innocent bystander. He has a strong sense of justice, so he would put himself in harm's way. It could be that a mutagen - affected creature is on a rampage in the city and Leo tries to stop it but underestimates its strength and gets hurt.
One common way is in a fight with a powerful enemy. Maybe a new mutant or a really tough Foot Clan member. Another way could be through some sort of accident, like a trap that was set for the turtles.
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.
One common theme could be the shock and confusion among the other turtles. They would have to deal with a situation that is completely out of the ordinary for their world.
Often in fanfiction where Leo is hurt, it involves him being poisoned. Maybe he gets hit with a dart laced with a slow - acting poison while on a mission. His brothers are desperate to find an antidote in time. This can lead to a lot of emotional moments as they search everywhere and Leo slowly gets weaker. They might have to seek help from unlikely allies, like some of the mutants they usually consider enemies.
One common scenario could be in a fight against a powerful new enemy. Maybe the enemy has some unique power that Gohan isn't prepared for, like a strange energy - based attack that can bypass his defenses and directly harm him. Another situation might be during a training session that goes wrong. His mentor could accidentally push him too far, resulting in an injury.
One common scenario could be during a dragon fight. Maybe Hiccup's dragon Toothless accidentally knocks him off during a tricky maneuver, leaving Hiccup with a sprained ankle or some bruises. Another situation might be when exploring new, uncharted lands. He could step on a hidden trap and get a leg injury. Also, in some fanfictions, he might be hurt while trying to protect his village from a new threat, like getting hit by a stray weapon.
One common scenario could be during a battle with the villains. For example, when facing the Serpentine, Jay might get caught by their venomous attacks which could hurt him badly. Another situation could be an accident while training with his fellow ninjas. Maybe he misjudges a move and ends up crashing into something hard, like a rock or a wall in the training area.
One common scenario is when Kagome is attacked by a demon while she's separated from Inuyasha. Maybe she's out gathering herbs or something and a lesser - known demon sees her as an easy target. Another situation could be when she gets caught in the crossfire during a battle between Inuyasha and a powerful foe. The enemy might target her to get to Inuyasha.
One common scenario could be during a mission. Maybe she gets caught in an explosion while trying to defuse a bomb. Another might be getting shot while providing cover for Macgyver. Or she could be injured in a fight with the bad guys when they manage to overpower her briefly.
Perhaps Leo is bullied in his neighborhood. There could be some older kids who target him when he's walking home from school or playing outside. They might take his things or push him around. This can make Leo feel scared and unsafe in his own neighborhood.