Board Thread:Support Requests - Community Management/@comment-3551372-20150701020125/@comment-452-20150701132127

Firstly, write rules which clearly state random off-topic comments are not permitted, and that anyone attempting to derail threads will be blocked.

Then block them. Put their heads on spikes and make it clear that that type of behaviour will not be tolerated.

You didn't specify: are these users worthwhile contributors in the first place? It seems unlikely that they would be.