CrushFTP watches the activity on the server, and if it detects a user abusing the server, it can automatically ban them for a specified amount of time. Its sort of like a robot babysitter for your server. The hammering command option applies to commands a user issues that return a failure command. Setting this too restrictive however can cause legitimate (but poorly designed) applications to get banned while they are "testing" to see if files exist. They may test for hundreds of files causing them to get banned if you set it too restrictive. Below these options is a list of currently banned IPs. You can remove items out of the list if they accidentally got banned. Adding an IP into the list will not automatically disconnect a user if they are currently connected, but will not allow them to reconnect if they did disconnect or got kicked.
Keep in mind the default "A" record is what allows any access at all. Without this record, all IPs are rejected. A=Allow, D=Deny. Minutes for the ban is how long until the ban expires, with 0 meaning it permanent and won't ever expire.