The Titans' Marcus Mariota has been one of the biggest mysteries of 2017. He was considered one of the NFL's best young quarterbacks a season ago when he threw for 3,426 yards with 26 touchdowns and nine interceptions, and ranked 10th in value per play among all quarterbacks, according to Football Outsiders. Now Mariota ranks 26th in value per play sandwiched between Eli Manning and Brian Hoyer, in what has amounted to a three-months-long string of disappointments.

Turns out, there may be an easy explanation for a lot of terrible football.

According to longtime Tennessee reporter Paul Kuharsky, Mariota's balky hamstring and surgically repaired lower right leg remain issues. Not only that, but the 2015 second-overall pick could require offseason clean-up surgery on the lower leg that was fractured on Dec. 24, 2016.

The Titans, who are 8-5 and currently the fifth seed in the AFC playoff race, lost an eminently winnable game to the Cardinals last Sunday. Mariota was just 16 of 31 for 159 yards with no touchdowns and two interceptions. The good news is that Tennessee controls its destiny. The bad news is that injuries have reduced Mariota to something less than the player he was a season ago and the Titans have regular-season games against the 49ers, Rams and Jaguars.

There's more bad news: This isn't just about Mariota; the entire offense has taken a step back and it's not clear how they can fix it in time to save their season.