Dennison attended J.P. McCaskey High School, where he was a district triple jump champion and finished sixth in the state finals.
[1] As a senior in 1973, he was leading the division in rushing, when he suffered a left knee injury in the fifth game of the season and was lost for the year.
Dennison was signed as an undrafted free agent by the Dallas Cowboys after the 1974 NFL draft, after not being selected because of his college knee injury.
[3] In 1976, he was named the starter after Pearson missed most of the season with an injury, leading the team in rushing (542 yards) and also scoring 6 touchdowns.
In 1978, he was placed on the injured reserve list, after suffering a left knee injury while playing special teams in the sixth game against the New York Giants.
[5] The Cleveland Browns signed him on October 13, 1979, to replace Greg Pruitt, who was lost for the season with an injured knee.
[11] After being out of football for three years, head coach George Allen signed him to the Chicago Blitz in 1983, to provide depth behind Tim Spencer.