Client hold is a domain registrar level freeze that is imposed at the registry, unlinke freeze where it is only at the registrar and dns resolution is not impared.
This can be done for many reasons, whois voilations, charge backs on renewals, transfer fraud, etc. Each registrar has its own laundry list of violations that would have to occur for this status to be incurred.
however it doesnt appear to be a problem any longer.