this is going to be a relatively straightforward list of things your character could do to get locked up in the skybox!

1 | theft
-medicine
-drugs
-extra rations
-clothes
-basically anything

2 | murder
-this one is dark
-you could have your OC be an actual murderer or maybe have them be falsely accused/framed
-in a more passive manner, like if they're a nurse in training and don't do everything they can to save a patient

3 | treason
-plotting against the chancellor
-maybe knowing about the error like clarke
-spreading false information and causing a panic

4 | vandalism
-the ark in general, or their more sacred items such as their trees
-maybe some graffiti for lols and then oops they get caught

5 | framing someone else
-maybe they allowed someone to take the blame for a previous crime and then were caught being the real criminal

6 | selling things illegally
-they probably had a black market
-they could buy things and sell them at a lower price

7 | violence
-attacking guards
-disorderly conduct (basically causing a scene)

basically any sort of crime that seems applicable on the ark can be used. it all depends on how much of a criminal you want your character to be!