Kidderminster have been leaving 3- 5 players "up" ready for the counter attack when defending corners. Its remarkably effective at reducing all that grabbling crap, as the attacking team have to leave some players back to defend. yes its risky, but generally as the attacking team will sent up their centre back fr the corner, if the defending team clears the first ball from the corner, suddenly there is a break on, against a "defence" in unfamiliar positions, so a good chance of a goal.
I think Chelsea maybe copied them a couple of times.