Watt didn't get enough help picking up sacks.
For the uninitiated, net yards per attempt is a derivative of the grandfather of all passing stats: yards per attempt (YPA). In actuality, YPA may be the single most telling stat in football.
Like its stately cousin, NY/A helps us understand what happens each time the quarterback drops back for a pass. For reference, NY/A is calculated by subtracting sack yardage from passing yardage, then dividing by passes attempted plus sacks. In other words:
(yards passing - sack yards) / (pass attempts + sacks) = Net Yards per Attempt
The question of what's wrong with Schaub has already been examined, but if you needed further evidence that his play wasn't up to its previous standard, NY/A will help illustrated it.
In 2011, Schaub averaged 7.7 yards per drop back, but that number dipped to 6.6 in 2012.
There are multiple components to the stat, however, so it's possible to determine where the issue was.
First, his completion percentage went up, so the problem wasn't accuracy.
Second, his sack rate went down, but his yards per sack increased by more than a yard. While that's interesting, it only affected his NY/A by 0.1. That's not nearly enough to account for his drop.
Finally, his throws down field were noticeably hampered. In 2011, Schaub had a passer rating of 125.3 on deep balls with no picks. In 2012, his rating on throws over 20 yards dipped to 72.0. He went from five touchdowns and no picks to six touchdowns and six picks. His YPA and completion percentage both dropped.
What caused Schaub's drop off was a mystery, but there's ample evidence the struggles were real.
For the record, Schaub's 2012 NY/A was still vastly superior to Yates' 2011 numbers.
Defensively, the Texans regressed from 2011. They dropped from second overall in NY/A to eighth. That's not a huge fall, and most of it was due to a reduced sack rate.
Despite J.J. Watt's epic season, the Texans simply were not as good at getting pressure as they were in 2011.
In 2011, players not named Watt accounted for 38.5 sacks for the Texans. In 2012, players other than Watt piled up just 23.5 sacks.
Connor Barwin, Antonio Smith and Brooks Reed led the 2011 Texans with 24 sacks. In 2012, the trio totaled just 12.5. Smith did his part, actually increasing his sack total, but Barwin labored and Reed battled injuries.
That kind of drop in pass-rush productivity will lead to defensive regression every time.