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 league has also made player safety recommendations to teams about drills that should no longer be used in training camp. The banned drills: Oklahoma, Bull in the Ring/King of the Circle, Half Line/3 Spot/Pods. The hope is this will drive down concussion numbers in camp.— Judy Battista (@judybattista) May 22, 2019
NFL has barred teams from using certain dangerous drills (Oklahoma drill, king of the circle, bull in the ring) during training camp. League will monitor and enforce that ban much in the same way that it deals with any violations of the offseason practice rules.— MarkMaske (@MarkMaske) May 22, 2019
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.