We don't want any running DHCP clients. You can read here about the reason to add this check.
It uses the command NRPE command /usr/lib/nagios/plugins/check_procs -w 0:0 -c 0:0 -C dhclient' on the affected host which you can run yourself.
So it expects exactly 0 processes called "dhclient" and any other number will create a CRIT.
You can manually check with "ps aux | grep dhclient" to look for the culprit. Kill the process.