The authoritative WInnForum reference for this topic is available in the most current version of WINNF-TR-5003 - CBRS Incumbent Protections and Encumbrances Overview, which you can access via this link. The rest of this article will complement what you read there. Refer to the attached Quiet, Exclusion, and Protection Zones technical note for details.
Incumbents – First Tier of CBRS
Incumbent Access users receive protection against interference from Priority Access Licensees and General Authorized Access users.
An exclusion zone is a geographic area where no CBSD shall operate, however the exclusion may only apply to specific frequencies. All exclusion zones are maintained and enforced by the SAS. When a CBSD is inside an Exclusion Zone or outside the Zone within 50 m of the boundary, the Grant will be denied.
Other times that a Grant will be denied:
Quiet Zones are areas in which it is necessary to restrict radiation so as to minimize possible impact on the operations of radio astronomy or other facilities that are highly sensitive to interference. There are several quiet zones around the United States.
Protection Zones are areas where CBSDs may operate, but may have their transmission power limited. For example, an FSS earth station without a GWBL located within a 150 km radius has a protection zone with a radius of 150 km around the earth station. CBSDs may operate in this area, but they are subject to having their transmission power reduced.