He finished his career with the Los Angeles Rams, the Green Bay Packers and the Houston Oilers.
[3] With Hadl running the offense, the Jayhawks were ranked in the top 20 during his junior and senior years, finishing 15–5–2.
[10] He joined the American Football League's San Diego Chargers in 1962, having decided to play with them over the Detroit Lions (who selected him in the first round (tenth overall) of the NFL draft).
[14] Although the Chargers won four games that year, they improved to eleven in 1963, owing to the acquisition of 35-year old Tobin Rote as the new starting quarterback.
[15] While Rote started each game, Hadl did take action in mop-up duty, throwing 28-of-64 for 502 combined yards and six touchdowns and interceptions.
Hadl went 6-2 while throwing for 2,157 yards on eighteen touchdowns and fifteen interceptions with a 53.6 completion percentage, and he was named an AFL All-Star.
However, in the 1964 AFL championship game, it was Rote who started against the Buffalo Bills and old teammate Kemp, now quarterbacking the opponent.
[20] In 1965, he was named San Diego's starting quarterback and led the team to a 9–2–3 record while throwing 2,798 yards (a league high) for twenty touchdowns and 21 interceptions and a 50.0 completion percentage, all good for a second straight AFL-All Star appearance.
[22] Hadl went 7–4–1 while throwing 2,846 yards for 23 touchdowns and fourteen interceptions for a 53.3 completion percentage, although the Chargers third-ranked offense was not enough for a playoff spot for the first time in four years.
He passed for 2,253 yards with ten touchdowns and eleven interceptions for a 48.8 completion percentage, and Hadl was named an AFL All-Star once again.
In his final year with the Chargers in 1972, he went 4–9–1, passing for 2,449 yards with fifteen touchdowns and 26 interceptions (a league high) while having a 51.4 completion percentage and a Pro Bowl selection.
Hadl was traded to the Los Angeles Rams in January 1973 for defensive end Coy Bacon and running back Bob Thomas.
He was named the National Football Conference (NFC) Player of the Year by UPI and selected to the Prow Bowl that season.
He went 7-of-23 for 133 yards with an interception as they lost 27–16 in a late fourth quarter rally in which the Rams were down by one point with ten minutes to go before the defense collapsed.
Hadl started the first five games for the Rams, then was replaced by James Harris during an upset loss to the Green Bay Packers in Milwaukee to fall to 3–2.
[30] Reportedly, head coach and general manager Dan Devine felt that an experienced quarterback was the only thing standing between the Packers and only their second playoff appearance since 1967, and it came about after an attempted trade for Archie Manning and the New Orleans Saints fell through.
[32] In later years, when asked for his thoughts on the infamous deal, Hadl himself expressed the surprise he felt, in 1974, at being sent to Green Bay: "I really didn't believe it...
"[33] Meanwhile, with a combined record of 6–5 on two teams, Hadl threw for 1,752 yards with eight touchdowns and fourteen interceptions and a 47.5 completion percentage.
Hadl was still on the top ten of most touchdowns thrown by a quarterback as late as 1999 (over twenty years after retirement), with him and two others in that list not being members of the Hall of Fame (Dave Krieg and Boomer Esiason being the others), as his former peak of fifth has receded to 26 with the advent of increased passing in subsequent years.
[36] Upon retiring as a player after the 1977 season, Hadl returned to his alma mater and served as quarterback coach under Bud Moore at the University of Kansas in 1978.
Hadl consistently denied any wrongdoing and his tenure with Kansas athletics hasn't yielded any suggestion of rules violations.