In 1989, Keith Millard had one of the most incredible defensive seasons ever, winning the AP Defensive Player of the Year and leading the NFL in Pro Football Reference’s Approximate Value metric. That year, Millard would record 18 Sacks, the third time he exceeded double digits in that statistic. He still holds the singles season record for Quarterback Sacks by a Defensive Tackle. Millard would be hampered by a severe knee injury that would hamper his effectiveness late in his career otherwise he would likely be higher on this list.