Colts banking on Andrew Luck putting 2015 behind him

Andrew Luck has signed the largest guaranteed contract in NFL history, according to ESPN's Adam Schefter. AP Photo/AJ Mast

The Indianapolis Colts announced Wednesday that quarterback Andrew Luck has signed a contract extension through the 2021 season. According to ESPN's Adam Schefter, the deal is worth $140 million with $87 million guaranteed. That is by far the largest guarantee ever given -- the previous high was $65 million to Eli Manning and Philip Rivers.

Luck has been one of the more prolific quarterbacks in his first four seasons in the NFL. He has the fourth-most passing yards by any quarterback in his first four NFL seasons, and he is the fourth quarterback with at least 100 touchdown passes through four years.

Luck started every game in each of his first three NFL seasons, and the Colts made the playoffs in each of them. Last season was a different story. Luck started just seven games; he missed two games with a shoulder injury and the final seven games with a lacerated kidney, and the Colts missed the playoffs.

Even when he was on the field in 2015, Luck was not very effective. He had a 55.3 completion percentage last season, the lowest of the 35 qualified quarterbacks. He averaged 6.4 yards per attempt, third worst among qualified quarterbacks, and his touchdown-interception ratio of 1.25 (15 TDs vs. 12 INTs) was a career worst.

Downfield success deserted Luck in 2015

He especially struggled throwing downfield, completing a league-worst 35.7 percent of passes thrown at least 10 yards, with 11 of his 12 interceptions resulting from those throws.

Luck had a Total QBR of 20.9 on those throws, worst in the NFL among qualified quarterbacks. In the 2014 season, Luck had a 91.8 Total QBR on such throws.

Six of those 11 interceptions on passes thrown at least 10 yards downfield were on throws intended for T.Y. Hilton. Overall, Luck had twice as many interceptions as touchdown passes when throwing to Hilton last season.

Luck had a 32.7 Total QBR when targeting Hilton last season. When targeting Hilton in 2014, Luck had a 94.1 Total QBR.

Feeling the pressure

Part of the reason for Luck's struggles last season was due to facing more pressure than he ever has. Luck was under pressure on 33.5 percent of his dropbacks last season, the fourth-highest percentage in the NFL. In his first three seasons, Luck was under pressure on 26.7 percent of his dropbacks.

The Colts used the NFL draft to bolster their offensive line. They drafted four offensive linemen in 2016 (no other offensive players), their most taken since 1983 (also four).