Nothing serious. We were training combat and we were given a small set of rules to get points which included (in hindsight) obvious holes. The smart guys quickly detected and exploited the holes, to the dismay of their opponents, some of whom got very angry. This was maybe 10 years ago, so one I remember: the rule was "a point if you slap your opponent shoulder with your hand", demonstrated as trying to hit the further shoulder of the opponent. It was a game of reflexes, keep the distance, quick entry and blocking, but also it was too easy to hit the closest shoulder, something someone noticed after a good two minutes into the exercise.
Before the e-hogus a fellow competitor used to punch in a way that was not damage effective, but made a lot of noise and looked like a real punch (almost like a backhand slap), scoring a lot of points. Their opponents claimed that they weren't even hit. Another guy used to launch kicks in the last possible moment of a clinch (almost always a jump-turning-and-back-kick, tuio mondollyo tuit chagi, don't know the name in english), just when he noticed in the corner of the eye the referee intended to break the clinch.
Before the e-hogus a fellow competitor used to punch in a way that was not damage effective, but made a lot of noise and looked like a real punch (almost like a backhand slap), scoring a lot of points. Their opponents claimed that they weren't even hit. Another guy used to launch kicks in the last possible moment of a clinch (almost always a jump-turning-and-back-kick, tuio mondollyo tuit chagi, don't know the name in english), just when he noticed in the corner of the eye the referee intended to break the clinch.