With the Events app, you can limit access to Ticket Types for a given event by user group. This includes limiting a Ticket Type to only back-end administrator users. Doing so can allow staff to register individuals for an event on the front-end of the site with free or specially-priced tickets.
Restricting access to Ticket Types to only back-end administrator users can be done even if your site does not have the Soapbox Portals add on feature that allows for a front-end user logged in experience.
For more on creating tickets and restricting access, check out Creating tickets for your Soapbox Event.
For more on the types of permissions for tickets check out Understanding Permission Types in restricting access to Event tickets.