The hole in county jail is not actually a hole, but a cell that is isolated from the rest of the jail population. Jails typically set aside a POD or area of the jail to house inmates who have been sentenced to solitary, a.k.a. the hole
Reasons for being assigned to solitary confinement:
If every jail fight caused inmates to go to the hole there would not be enough cells to hold them all, but for serious fighting it is used to control the situation.
For example, during a fight one or more inmate was injured and required medical care. If the investigation reveals which inmate was the primary aggressor he will be sent to the hole as punishment.
Check out: A Controversial Punishment
Hitting a guard:
This results in being put in the hole as well as being charged with assault
on a correctional officer.
Refusal to obey commands:
Inmates who refuse to do as the correctional officers tell them to do are put in the hole to teach them a lesson. They also are used to serve as an example to the rest of the jail population with regard to doing as they are told.
In most cases, the inmate assigned to the hole knows how long he will be there. However, there are scenarios where it is indefinite.
Many counties have rules on how often an inmate in the hole
must have an administrative hearing to determine whether the punishment should continue or be finished.