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Andrew Luck has regressed in a way nobody saw coming.
Luck was expected to dominate in 2015, rounding into one of the NFL's best quarterbacks while turning the Colts into true Super Bowl contenders.
Instead, Luck is having arguably the worst season of his career, and the Colts are 3-4.
Through five games, Luck is 1-4 as a starter and is posting numbers comparable, or worse, than his rookie season. He has a 56% completion rate (second-worst in his career), nine interceptions with a 4.3% interception rate (worst of his career), a 76.3 passer rating (worst of his career), and is averaging 6.7 yards per pass attempt (worst of his career) and 11.9 yards per pass completion (second-worst of his career).
It seems clear that part of the problem is that Luck is still hurt. The Colts were oddly tight-lipped about Luck's injury two weeks ago, but it became clear Luck wasn't right when they started 40-year-old Matt Hasselbeck over him, just two days after Hasselbeck was in the emergency room with a virus.
Luck came back in Week 6 and had a decent showing against the Patriots, but in Week 7, he was miserable against the Saints. Much of his 333 yards and all three touchdowns in the second half when the Colts trailed by double-digits. Games like this make Luck's 5.2% touchdown rate, the second best of his career, misleading.
In fact, For the Win's Chris Chase found an odd stat on Luck. Luck has thrown 28% of his touchdowns when the Colts are ahead or behind by 17 or more points (meaning the trailing team needs at least three scores), far more than many of his peers. In other words, many of Luck's touchdowns come when the game isn't on the line, and in a sense, they don't matter.
While it's common to blame Luck's supporting cast, that argument is flimsy this year. Luck has a talented group of receivers in T.Y. Hilton, Andre Johnson, Donte Moncrief, and Phillip Dorsett, and while his options at running back aren't the best, you can do much worse than Frank Gore, who still has 446 rushing yards this season.
The offensive line is also not entirely to blame either. They don't help matters, of course - Luck's 5.4% sack rate is way up from last year, but not far from his 5.3% rate in 2013 and 6.1% in 2012. However, according to Football Outsiders, the Colts' offensive line has been fine in pass protection. Through six weeks, they ranked 11th in pass protection, with a 5% adjusted sack rate (sacks adjusted for intentional grounding penalties as well as down, distance, and opponent). By this metric, Luck has had better protection than quarterbacks like Aaron Rodgers, Philip Rivers, Ryan Tannehill, Cam Newton, and Russell Wilson.
If we move past the idea of blaming all of the struggles on an injury, Luck's regression is baffling. As CBS's Jason La Canfora wrote: "[Luck's] regression is very real. Luck looks disjointed and impatient and his shoulder is probably still bothering him, but even still, some of his decisions with the football look rookie-worthy."
La Canfora pointed specifically to this play, in which Luck's choice to throw to a well-covered section of the end zone was confusing:
"I'd say I'm frustrated up here. I think as a unit, we're frustrated and I'm frustrated with myself. Some egregious turnovers, especially the one at the end of the half. It's really bad football... I've got to play better. I'm sure everybody in the locker room will say the same thing, but I've got to play better."
While a bothersome shoulder could sap Luck of arm strength and accuracy, his decision-making and inability to make use of an improved supporting cast is the oddest factor yet.
The Colts' only saving grace is that they play in the worst division in football, the AFC South, which they lead with a 3-4 record. However, in the coming weeks, they'll face the Panthers, Broncos, Falcons, and Steelers. If they're falling behind by three scores to the Saints, they could be in real trouble if Luck isn't better by the time they're facing actual playoff teams.