For a prevention of flood requests to a web site, we assume a unfriendly would request two pageviews per second.
So, our time interval to check for a friendly is 10 seconds and 20 pageviews or 2 pageviews per second.
If they request 20 pageviews within 10 seconds the system dies (exists) with a warning. After the time interval has been reset the user then has two additional attempts.
After the third warning that user's session is banned.