At the NFL owner's meetings on Wednesday, the league voted to ban three drills from being used during training camp, hoping to tamp down the risk of concussions during camp. According to several reports, those drills are: Oklahoma, King of the Circle/Bull in the Ring, and Half Line.

The Oklahoma drill is a familiar one, where an offensive lineman and defensive lineman square off in the trenches as a ball-carrier attempts to skirt past the defender while staying within a narrow area defined by two blocking pads. (Note that we're using college film because most NFL teams don't release footage of these drills.)

The King of the Circle drill, also called Bull in the Ring, is similar, except it involves the two players competing to either take each other to the ground or push each other out of a circle. 

The half-line drill is exactly what it sounds like: they use only half of an offensive and defensive line and run some plays.