The yard in the NFL for clipping is fifteen (15) yards. The penalty is assessed fifteen yards from the previous line of scrimmage. In Football, clipping occurs when an offensive player blocks a defensive player from behind, which often occurs below the waist.
Clipping is most often not allowed due to its great potential to cause injuries to the collateral and cruciate ligament. The National Collegiate Athletic Association (NCAA) was the first to ban clipping and this occurred in the year 1916. Over the years, new rules and regulations were put in place by many leagues to prohibit clipping.