@fluffy4 - While some graduate assistants do get reassigned to a different department, it's never too far away from the original field of study.
For example, someone with an English degree might get assigned to the sociology, anthropology or psychology department. Those are also fields that require a lot of writing and the undergrad students could benefit from someone with a strong writing background.
Someone with a degree in history might get assigned to the political science department because that graduate student would know a lot of the history that went into creating the U.S. government and its laws.
There will always be a connection between the grad student's field and their assigned department.