The Switch Ports will go into a blocking state at the time of election process, when a switch receives a BPDU on a port that indicates a better path to the Root Switch (Root Bridge), and if a port is not a Root Port or a Designated Port.
A port in the blocking state does not participate in frame forwarding and also discards frames received from the attached network segment. During blocking state, the port is only listening to and processing BPDUs on its interfaces. After 20 seconds, the switch port changes from the blocking state to the listening state.