[12][13]) As a track star, Jackson won seven Southwestern Athletic Conference championships, four in discus and three in shotput.
[17][18] The Broncos switched him to defensive end and Jackson showed the quickness that was to become his trademark in professional football.
[1][17] Though typically double and triple teamed by opposing blockers, he believes he had more sacks than have been unofficially estimated.
[21] During his time in the NFL, Jackson's nickname was "Tombstone," and he became famous for moves such as the "head slap" and the "halo spinner" which he used to subdue opposing offensive linemen.
In Lyle Alzado's book "Mile High" he recalled Jackson as the toughest man he had ever met, and told the story of Jackson breaking the helmet of Green Bay Packers offensive tackle Bill Hayhoe with a head slap.
He split the man's helmet, drove him to his knees with a bloodied face, leaving Hayhoe to be helped off the field.
[1][17] He was named 1st Team All-AFL by the Associated Press (AP), Pro Football Weekly, and United Press International (UPI) at the conclusion of the 1968 season,[25] and by the AP, Newspaper Enterprise Association (NEA), New York Daily News, Pro Football Weekly, The Sporting News, and UPI at the end of the 1969 season.
[1] Jackson's career was cut short by a severe knee injury midway through the 1971 season in a game against the Philadelphia Eagles.
[2][28] Despite the shortened career, Sports Illustrated's football expert, Paul Zimmerman, said that Tombstone Jackson was perhaps the finest overall defensive end and pass rusher he ever saw, a surefire Hall of Famer if he would have had a longer playing career, in a bigger media market.
Zimmerman grouped Jackson with all-time great Deacon Jones[29][30] at defensive end, having the highest level of competitiveness and athleticism.
[17][2][29] Jones, whose autobiography is entitled Headslap, himself admitted he did not invent the head slap, which may have originated with his Los Angeles Rams teammate Roosevelt Grier, but like Jackson considered himself to have developed and mastered the tactic.
He was inducted in 1984 along with safety Goose Gonsoulin, running back Floyd Little, and wide receiver Lionel Taylor.
[38] In 2015, the Professional Football Researchers Association named Jackson to the PRFA Hall of Very Good Class of 2015.