A Texas Christian University Horned Frog in college, Lyle Blackwood was drafted in the ninth round of the 1973 NFL Draft by the Denver Broncos, 217th overall.
Blackwood failed to catch on with the Broncos, getting cut in training camp. He hooked on with the Cincinnati Bengals later that season, appearing in seven games. He would stay with the Bengals for three seasons, mostly as a punt return man, appearing in a total of 34 games.
In 1976, Blackwood joined the expansion Seattle Seahawks as their primary punt returner, running back 19 for 132 yards.
In 1977, Blackwood moved on to the Baltimore Colts, leading the NFL with 10 interceptions and returning them for an NFL second best 163 yards. He ended up playing four seasons in Baltimore altogether, appearing in 57 games for the franchise and intercepting a total of 19 passes.
Blackwood would join the Miami Dolphins prior to the 1981 season, joining younger brother Glenn in the defensive secondary. Glenn would play strong safety, while Lyle covered the free safety spot. The two came to be known as "The Bruise Brothers," and later, an important part of "The Killer B's." Lyle intercepted three passes in the 12 games in which he appeared that season.
In 1982, the season was cut down to nine games due to the players strike. Lyle started all nine games, and all four playoff matchups. He intercepted two passes in the regular season, then one against the San Diego Chargers in the Divisional Playoffs and another in the Dolphins losing effort in Super Bowl XVII.
The Dolphins won the AFC East Division title in 1983 with a 12-4 record. Lyle intercepted four passes that season in starting all 16 games plus the divisional playoff loss to the Seattle Seahawks.
Miami would return to the Super Bowl following a 14-2 1984 regular season on the back of passing records by Dan Marino and "The Marks Brothers," and continued shut down defense from Blackwood and the Killer B's Lyle again started every game, intercepting three passes and recovering two fumbles for the Dolphins.
After two more seasons Blackwood would retire a 14 year NFL veteran, the final six with Miami. He totalled 74 games for the Dolphins, starting 55 at the free safety position and intercepting 14 passes with five fumble recoveries.