This is a systematised breach of Play the ball, not the man rule. It happens only sporadically on Slugger, but its intention is to uses the anonymity of the commenting zone to attempt to damage the reputation of some known public figure: politician; journalist; key witness; or even individual bloggers.
The strategy was first outlined by L Ron Hubbard in 1965 as Fair Game Law. Hubbard’s target was in his own terms, ‘suppressive people’:
Suppressive Acts are clearly those covert or overt acts knowingly calculated to reduce or destroy the influence or activities of Scientology or prevent case gains or continued Scientology success and activity on the part of a Scientologist.
As persons or groups that would do such a thing act out of self interest only to the detriment of all others, they cannot be granted the rights and beingness ordinarily accorded rational beings and so place themselves beyond any consideration for their feelings or well being. [Emphasis added]
[Update 2015]: It has become a pretty widespread phenomenon on social media.