In 2014, the Houston Texans took a huge step forward from their 2-14 2013 season, going 9-7 and finishing second in the AFC South, just missing the playoffs.

They looked to build on this success going into 2015 but had to deal with some big personnel changes.

Their offseason losses included their starting quarterback in Ryan Fitzpatrick, top wideout Andre Johnson, a starting offensive lineman in Chris Myers, and one of their better linebackers in Brooks Reed.

They looked to cover up the offensive losses with the additions of Brian Hoyer, Cecil Shorts and Nate Washington and made an effort to shore up their defense with the addition of Vince Wilfork.

The offseason didn't seem to change a lot in either direction, and Houston once again finished 9-7 in 2015, winning the AFC South and losing in the Wild Card Round to the Kansas City Chiefs.

Let's take a look at how that 2015 season played out.

What Went Right?

If you're looking for the reason that Houston was able to win nine games and their division despite their parade of poor quarterbacks, you don't have to look any further than their defense. Their huge jump from 2013 to 2014 came on the back of the league's top defense, and that unit carried them once again in 2015.

Here at numberFire we have a metric called Net Expected Points (NEP) which measures how many points are contributed compared to expectation level (you can read more about NEP in our glossary). The Texans' defense finished the 2015 season ranked 10th in Adjusted Defensive Rushing NEP per play (when adjusted for strength of schedule), 3rd in Adjusted Defensive Passing NEP per play, and 3rd in overall defensive efficiency.

To the surprise of nobody, J.J. Watt devastated opponents all season. He deflected 8 passes, forced 3 fumbles, tallied 57 tackles, and a league-high 17.5 sacks en route to yet another Defensive Player of the Year award.

Watt had plenty of help in keeping opposing offenses in check as well.

Whitney Mercilus really stepped up his production this year, recording double-digit sacks for the first time in his career with 12.0. The duo of Mercilus and Watt are a big part of why the Texans' pass rush finished as one of the best in the league, averaging a sack every 13.57 opposing drop backs, the fourth-best mark in the league.

Also contributing at a high level on their defensive front was the newly-acquired Wilfork. It was no surprise that he didn't contribute much as a pass-rusher, but he had a big impact, anchoring their 10th-ranked run defense.

In the secondary, Johnathan Joseph really stood out with a terrific season. He was the top corner in their third-ranked pass defense and finished fourth in the league with 22 pass defenses.

There weren't as many highlights for Houston on the offensive side of the ball, but the biggest, most obvious one was DeAndre Hopkins who made the jump from a solid receiver in 2014 to an elite one last season.

Largely as a result of the poor quarterback play in Houston, Hopkins wasn't exceptionally efficient on a per-target basis, ranking 34th among the 86 receivers to see 50-plus targets on the year with a 0.75 Reception NEP per target, but he caught 111 passes for 1,521 yards and 11 touchdowns, and his 143.89 total Reception NEP ranked fourth in the league.

What Went Wrong?

Outside of Hopkins, just about every aspect of the Texans' offense we can look at was a negative for 2015.

Losing Fitzpatrick hurt, and the replacement quarterback play was awful. The Texans had three passers record at least 50 drop backs on the year: Ryan Mallett, T.J. Yates and Brian Hoyer.

Looking at the Passing NEP per drop back for each of them gives us a good idea of how ugly things were. There were 51 quarterbacks in the league with at least 50 dropbacks, and of that group, Hoyer lead the Texans, finishing 20th, Yates ranked 36th, and Mallett (excluding his games with Baltimore after being cut) ranked 44th.

Not providing any respite from the passing struggles, the Texans also boasted one of the worst rushing offenses in the league, ranking 24th in schedule-adjusted Rushing NEP per play.

Bell-cow running back Arian Foster sustained a groin injury leading up to the season, creating serious questions about his availability for the year, but he was able to return in Week 4. He managed to play in only four games before tearing his Achilles tendon, ending his season.

He was hugely ineffective even when he was on the field, and his -0.24 Rushing NEP per carry was the second-worst mark among the 72 backs to record at least 50 carries on the year.

They didn't have much success replacing Foster with Alfred Blue or Chris Polk either, as Polk ranked 60th among that group, and Blue led the team by finishing a mere 57th.

This horrendous rushing attack not only reflected poorly on the stable of running backs but also brought to light an offensive line that really struggled with run blocking.

What's Next?

Houston has already made a big splash in free agency in an attempt to shore up some of the big holes in the offense, signing quarterback Brock Osweiler and running back Lamar Miller.

Osweiler ranked 22nd among the 37 quarterbacks with at least 200 drop backs this year in Passing NEP per drop back, but he was playing in his first real game action of his career, and the Texans will be banking on him to continue to improve, becoming a quarterback who can lead them deep in the playoffs.

Miller ranked 28th among the 72 50-plus carry backs with a -0.01 Rushing NEP per carry, a far better number than any Texans back managed last year. He may not put up the same numbers if the offensive line continues to struggle, but they have undeniably made an upgrade at the running back position.

The defense has already shown that it's a strong enough unit to carry the team to the playoffs, and it won't take much to improve on last year's offensive performance.

If Osweiler and Miller can click with the offense right away, the Texans are quietly a threat to make a deep playoff run in 2016.