Accidents listed here are caused by one of the following:

Negligence on the part of the guest. This can be refusal to follow specific ride safety instructions, or deliberate intent to violate park rules.

The result of a guest's known, or unknown, health issues.

Negligence on the part of the park, either by ride operator or maintenance safety instructions, or deliberate intent to violate park rules

And clicking through the links, they generally add:

Act of God or a generic accident (e.g. slipping and falling), that is not a direct result of an action on anybody's part.