Kick a single user out of the database
As a one-off you can use EXEC sp_who or EXEC sp_who2 or similar to find the SPIDs of that user's connections and then use KILL &lt;SPID&gt; to stop them. Be aware that any transactions they have open in which changes have been made will need to be rolled back which could potentially take some time and be I/O intensive, but if they are just running reports the effect of this should be minimal. To stop them immediately restarting the processes disable their access before doing this (using ALTER LOGIN &lt;name&gt; DISABLE or by adjusting their access rights more granularly).

If you find yourself needing to do this regularly you could write a procedure to automate the task, so you could just run EXEC kick_user_off '&lt;name&gt;';, though if you need to do this sort of thing regularly enough for it to be worth the effort automating then I suspect you have a process and/or user problem that needs fixing of which this is just a symptom.