You probably didn’t know it, but Cam Newton is having a down year, at least statistically.

Carolina’s defense has been outstanding, of course, so an 8-3 record and a seven-game winning streak have overshadowed any flaws in Newton’s game. The Panthers have held an average lead of 5.05 points per second this year, the third best rate in the league. As a result of that high Game Script, Newton is asked to do less on offense, but that doesn’t explain the declining efficiency numbers. Newton’s taking slightly more sacks and his rushing numbers are down across the board, but the biggest decline comes with respect to yards per completion.

After lead the league in that metric a season ago, Newton is averaging just 11.3 yards per completion this year, the 23rd best rate among qualifying passers. As a result, Newton is posting career lows in yards per attempt, net yards per attempt, and Adjusted Net Yards per Attempt.

Yards per attempt and the many variations thereof don’t tell the full story, of course. Carolina is running a more horizontal, move-the-chains style of offense, and it’s working: the Panthers rank 4th in drive success rate, and only 49% of Carolina drives have ended in a turnover or a punt, the 6th-best rate in the league.

Still, it’s not good to lose a full yard off of a passer’s average throw. Can we figure out why? The table below breaks down the Panthers targets from 2011 to 2013 into four groups: Steve Smith, the rest of the wide receivers, the tight ends, and the running backs. For each row, I’ve included the average yards per target gained on throws to that group, with the percentage of targets next to that number in parentheses.

As it turns out, the biggest reason for Newton’s decline in yards per attempt is on throws to Smith: while the star wideout has continued to receive between 25 and 29% of all Panthers targets, his yards per target average has dropped significantly in 2013. Even as a proud member of the #89 fan club, I can recognize that those are some ugly numbers.

This season, all NFL wide receivers are averaging 7.76 yards per target. I’m not a fan of using yards per target data generally, and I wouldn’t advocate using the following as much more than trivia, but I thought it would be interesting to look at which receivers have produced the most and fewest yards over average per target. For example, DeSean Jackson has 985 receiving yards on 89 targets, an 11.1 Y/T average. Considering the “average” receiver would gain 691 yards on 89 targets, Jackson has produced 294 yards over average this year, the highest rate in the league. Below are the top ten receivers in yards over average.

And, more relevantly, the bottom 10:

Again, there are many issues with using a statistic like yards per target, but Smith is obviously not putting himself in great company. That list consists of players with terrible quarterbacks, talented receivers having down seasons, and bad/rookie wide receivers. And, of course, Smith. So let’s investigate further. Why is Smith’s yards per target average so low? It’s not because of his catch rate, which at 56% is in between where it was in 2011 and 2012. But after averaging 16.9 yards per catch during Newton’s first two years, Smith’s averaging just 11.4 yards per grab this season. That’s why Smith is averaging just 53 yards per game, the third lowest average of his career behind only his rookie season and the Jimmy Clausen season.

We can also break down Smith’s declining yards per completion average, too. In 2011, Smith averaged 17.65 yards per catch, thanks to averaging 11.84 yards per catch through the air and 5.81 yards after the catch. Last season, Smith’s 16.08 YPC average was based on averaging 12.41 yards per catch through the air and 3.67 yards after the catch on each reception. This year, Smith is averaging only 8.51 air yards per catch and 2.88 yards of YAC per catch. Last year, Smith ranked 5th among the top 100 most targeted players in air yards per catch (behind only Vincent Jackson, Lance Moore, Torrey Smith and Malcom Floyd); this year, he’s tied for 41st.

I noted at the top of the post that the Panthers ran a much more vertical offense under Rob Chudzinski than the team does under Mike Shula. That’s reflected in the fact that Smith’s air yards per catch is way down. But the problem is his catch rate — while on the surface not declining — is really ugly in that regard.

Reggie Wayne (9.1 Air Yards/Catch) caught 65.5% of his targets before his season-ending injury; Antonio Brown (8.0) is at 69% in Pittsburgh’s horizontal offense. Keenan Allen (9.2) is at 70%. Dez Bryant (8.2) is at only 58.1%, but he makes up for it by averaging 5.5 yards after the catch per reception. Anquan Boldin has a 63% catch rate despite his averaging reception being 9.6 yards down the field and despite the struggles of Colin Kaepernick. Posting a sub-60% catch rate while running short routes is not good.

Does that mean this is the beginning of the end for Smitty? I don’t know. It’s certainly possible that Newton is as much or more to blame for the duo’s struggles than Smith. And it could just be a slump — there’s still time for Smith to finish the year strong. But I do think it’s interesting that the two Panthers offensive stars seem to be having down years while the hype around the team has never been higher.