San Francisco 49ers: Adapting Stevie Johnson's Stats to San Francisco's Offense

How good is Stevie Johnson, the new receiver for the San Francisco 49ers?

Pretty good, certainly.  Before last year, when he missed four games with a variety of injuries and nagging problems, Johnson had gone over 1,000 yards receiving in three straight seasons.  While he’s never quite been a Pro Bowl-caliber player, he’s been a consistent contributor over the last four years:

Year	Rec	Yds	TD
2010	82	1,073	10
2011	76	1,004	7
2012	79	1,046	6
2013	52	597	3

Since he became a full-time starter in 2010, Johnson’s averaging 62 yards per game, which is 30th in the league over that period.  He fits in snugly between Anquan Boldin’s 62.7 yards per game and Michael Crabtree’s 57.8; he’s consistently been the leading target for the Buffalo Bills, and he looks ready to bring that talent over to the 49ers.

However, his raw numbers only tell part of the story.  See, Johnson hasn’t been catching passes from players like Alex Smith and Colin Kaepernick over the last three seasons.  The level of quarterback play he’s had to deal with has been significantly worse.

Quarterback	Targets	Completions	QB Rating
Ryan Fitzpatrick	281	154	81.0
E.J. Manuel	70	34	77.7
Thad Lewis	24	12	81.0
Jeff Tuel	7	5	45.1
Tyler Thigpen	1	1	26.1
Alex Smith	0	0	95.1
Colin Kaepernick	0	0	93.8

Some of Johnson’s numbers, then, might be depressed because he’s been playing with sub-par quarterback play over the past few seasons.  Had he been in a better offensive environment, Johnson’s numbers would have been higher.

That point inspired Nate Silver of FiveThirtyEight to try to figure out how top receivers’ stats would look if they had played with a league-average QB.  Some players have benefitted hugely from playing with great quarterbacks, like Jimmy Graham has due to catching passes from Drew Brees.  Others have had to make do with whatever quarterback a team could throw out there, like Cleveland’s Josh Gordon.

What he’s done is take a look at a statistic called Pass EPA.  Essentially, what this does is calculate the value of each pass in terms of how successful the play is, rather than just the raw yardage it gains.  It factors in the down and distance, as well as the field position, to calculate the value of every play.  For example, a four-yard gain on 3rd-and-3 is much more useful than a four-yard gain on 3rd-and-8.

Jeff Roberson/Associated Press

By this metric, the most successful quarterback in 2013 was Peyton Manning, who added 248.3 points based on his passing performance last season, while Kirk Cousins cost Washington 39.9 points with his play.  On a per-play basis, Colin Kaepernick was the seventh-best quarterback in football, adding 0.16 points per pass.  By comparison, Buffalo’s best quarterback (Thad Lewis) scored exactly 0 by this metric, while E.J. Manuel put up -0.07 points per pass.

What Silver did was use advanced mathematical techniques to try to factor out the effects of the quality of quarterback play, and try to calculate how a player would have done with a league-average player.  I can’t exactly replicate his work, as he used ESPN.com’s version of the statistic, which isn’t publicly accessible.  I can, however, report his results here:

Situation	Rec	Yds	TD	Fantasy Points
Reality	69	882	5	189
W/ Average QB	75	997	7	217

Essentially, Johnson lost about 115 yards a season, just from having to handle the low-caliber quarterback play in Buffalo.  It’s actually even a little worse than the raw stats appear, too.  These are average numbers, but Johnson missed time in 2013, which would depress his stats.  Run the same calculations over his last three full seasons, and you’ll add an extra 10 to 15 yards or so to those totals.

But Johnson won’t have average quarterback play in San Francisco; the passing game has actually been consistently above-average on a play-by-play basis, if not in terms of gross yardage.  Silver did the same regression for 50 of the top receivers, including two 49ers:

Situation	Rec	Yds	TD	Fantasy Points
Vernon Davis	53	730	8	174
Davis w/Average QB	52	704	7	166
Michael Crabtree	59	754	5	162
Crabtree w/Average QB	57	722	4	153

Essentially, it appears playing in Buffalo the last three seasons costs a receiver about eight percent of their potential receptions, 12 percent of their receiving yards and 29 percent of their touchdowns.  That’s not as bad as playing in Cleveland, but it’s a pretty large dampening effect.

Conversely, playing in San Francisco the last three years would account for three percent of their receptions, four percent of their receiving yards and 18 percent of their touchdowns.  It’s not exactly Peyton Manning territory, but it’s a notable boost.

Translating Stevie Johnson’s stats to San Francisco the last three seasons, then, would give you something like this:

Situation	Rec	Yds	TD	FP
In Buffalo	69	882	5	189
w/ Average QB	75	997	7	217
In San Francisco	77	1,038	8	229

This is obviously a very rough, back-of-the-envelope calculation, but it’s promising nonetheless.  Those are very close to the numbers Larry Fitzgerald has been putting up—his average over the last three seasons has been 78 receptions, 1,054 yards and seven touchdowns.

Matt York/Associated Press

Am I saying that Johnson is secretly as good as Larry Fitzgerald?  No, of course not—put Fitzgerald in San Francisco, and he’s probably earning an extra 200 yards a season, simply due to superior quarterback play.  All I’m really trying to say is that our perception of Johnson’s ability should take into account the fact that he’s entering a much better offensive environment than he’s had to deal with during his career.

As the third receiver behind Michael Crabtree and Anquan Boldin, and with a talented tight end like Vernon Davis in town, Johnson will have trouble putting up volume stats to match what he has done in Buffalo.  It’s a little tougher competition than Scott Chandler, Fred Jackson and C.J. Spiller.

Still, with higher-quality play on his side in 2014, as well as a return to health, Johnson should bounce back to have a very successful season in San Francisco.

Bryan Knowles is a featured columnist for Bleacher Report, covering the San Francisco 49ers.  Follow him @BryKno on twitter.