Maybe it was an accident caused by one of his own team members. For example, if Chase was working on a new invention and there was an unforeseen error that affected Adam when he was nearby. It wasn't intentional, but it still led to Adam getting hurt.
In some cases, it could be a side - effect of a scientific experiment gone wrong at the lab. The scientists were trying something new and risky, and Adam, being one of the test subjects, ended up getting hurt as a result.
Another situation might be that Adam gets hurt in a training accident at the lab. He could be trying out a new high - risk training exercise and something goes wrong. Like, if they were testing a new type of gravity simulator and it malfunctioned, throwing Adam around and causing him physical harm.
There's also the theme of vulnerability. Adam is a strong character in the show, but when he's hurt, it reveals his vulnerable side. Fanfictions might explore how he deals with this new - found vulnerability and how those around him react to it.
In some fanfictions, Adam could get hurt accidentally in the lab. For example, there could be an experiment malfunction that causes him to be injured. This could lead to a story about the scientists trying to find a way to heal him, and Adam's own struggle with being temporarily incapacitated and relying on others.
Sometimes, it could be due to her own actions. Lydia might be overconfident and take risks that she shouldn't. For instance, she could try to perform a very difficult and dangerous magic spell without proper training, and it backfires, causing her to get hurt.
It could be a villain in the fanfiction. Maybe a new, powerful vampire who has a vendetta against Bella or her friends.
Another character who might be responsible is a jealous rival. This person could be envious of Elena's popularity or her relationship with someone important. So, they set a trap that causes her to get hurt.
In the fanfiction, it might be someone from his own team. Maybe there's a new member who is insecure and feels that Kuroko is getting too much attention. So, in a fit of jealousy, this person does something that causes Kuroko to get hurt, like tampering with his equipment.
A new villain in the story could be responsible. This villain could be out to make a name for themselves by taking down Harley.
Perhaps an unknown ice sorcerer. Since the Frozen world has magic, a new character who is jealous of Elsa's power could target Anna to get to Elsa. They might use their ice powers to create dangerous situations for Anna, like making the ice floor slippery and causing her to fall and get hurt.
It could be Vilgax. He's one of Ben's most powerful enemies. Vilgax is always looking for ways to defeat Ben, and he might come up with a new and devious plan to hurt him. Maybe he teams up with other villains to ambush Ben when he's least expecting it.