The legal concept that opens the way for vicarious liability is "respondeat superior," which is the establishment of a relationship between the principal defendant and the target of vicarious liability that implies responsibility for the principal defendant. In the case of an employee who does harm or commits negligence that causes harm while on the job, the employer can be found vicariously liable if what the employee was doing was in the conduct of his responsibilities.
In most cases, the actions of an independent contractor cannot lead to a vicarious liability lawsuit against the employer who contracts with the independent contractor. The exception to this rule is when the independent contractor is serving in the same manner as an employee -- that is, when not only the outcome of the work is under the employer's control but the conduct of the work itself.
If an employer directs the contractor on how she does the job, the law says that contractor is an "employee," or servant. If the employer only checks to see the outcome of the work and has no supervisory control over the conduct of the job, that employer is not subject to vicarious liability for offenses by the independent contractor.
Actions by an employee that are not within the scope of the job do not generally expose the employer to vicarious liability lawsuits. For his actions to qualify as within the scope of employment, the primary offender must be doing what his employer has directed. The offense or neglect must occur in a time and place designated for work. If the offense includes the use of force, the plaintiff will have to show that the use of force was not unexpected by the employer.
Besides suits for damage that occurred to someone outside a firm, vicarious liability lawsuits are available to one employee against an employer based on what a fellow employee -- especially a supervisor -- has done. This is common in sexual and racial harassment lawsuits. In this case, the plaintiff must first show that there was a discriminatory practice according to civil rights statutes; only then may a suit be brought against a vicarious defendant.