It's the No. 1 difference at receiver

Last season Michael Crabtree played all 16 games for the San Francisco 49ers, and he was what he always has been: a possession receiver with 68 receptions, a 10.3-yard average and four touchdowns.

The 49ers let him walk in free agency without a fuss.

This season with the Oakland Raiders, Crabtree has 70 receptions, an 11.1-yard average and seven touchdown with three games still to play. Little more than a week ago he signed a four-year contract extension that will pay him $11 million next year and averages $8.5 million a season.

Last season, Randall Cobb set career highs in receptions (91) and touchdowns (12), and averaged a robust 14.1 yards a catch. Just before the start of free agency, the Green Bay Packers re-signed him to a four-year deal that included $15 million in first-year pay and averages $10 million.

This year, with three games to play, Cobb has 65 receptions, an 11.3-yard average and only six touchdowns.

Thus, from opposite ends, we see the value of a true No. 1 receiver in the NFL.

For the Raiders, it was general manager Reggie McKenzie adding a bona fide No. 1, Amari Cooper, with the fourth pick of this year’s draft. Crabtree's value went up the first time Cooper stepped on the field.

For the Packers, it was losing their No. 1, Jordy Nelson, to a season-ending knee injury in the preseason. They’ve since found out the limitations of their other receivers, including Cobb. He’s a difference maker as a No. 2, but a player defenses can take out of games as a No. 1.

You can’t measure receivers such as Nelson or Cooper – provided they have the quarterback play – on their numbers alone. What makes them true No. 1s is that even when defenses try to take them out of the game, they more often than not get theirs, and while they’re occupying extra attention, the rest of the pass-catching corps benefits.

“People have to look for (a No. 1) and account for him,” said Dom Capers, the Packers’ defensive coordinator. “Obviously, if you commit two to him you have everybody else singled up.”

The Packers will face Cooper for the first time as an NFL player Sunday, and to get a sense of Cooper’s impact on the Raiders, start with the basic numbers. Last year, they ranked No. 31 in the NFL in scoring and No. 32 in yards. This year, they’re Nos. 12 and 15.

Cooper doesn’t deserve all the credit – quarterback Derek Carr’s improvement in his second NFL season can’t be undersold. But he has proven to be the rare rookie receiver who tilts the field.

His 62 receptions leads all rookies and is tied for No. 26 overall. His 14.8-yard average ranks No. 13 among players with 50 or more catches.

Cooper has decent size (6-feet-0 7/8, 211 pounds) and the kind of speed that can change games (4.34-second 40). A scout from one of the Raiders’ rivals in the AFC West said Cooper has comparable skill and explosiveness to one of the NFL’s top young receivers, the New York Giants’ Odell Beckham Jr.

“(Cooper) is pretty dang talented,” the AFC West scout said. “With the ball in his hands he can hurt you pretty good. He can score in the red zone or he can take the ball 80 yards on a slant. Closer to Beckham as far as making people miss and being electric as opposed to those big, fast guys like (Atlanta’s) Julio (Jones) or (Cincinnati’s) A.J. Green.”

Compare Cooper’s numbers with last season, when the Raiders’ No. 1 receiver was James Jones, who had 73 receptions but for only a 9.1-yard average. He didn’t threaten defenses in any way.

The Raiders signed Crabtree in mid-April, selected Cooper in the draft and then cut Jones in mid-May. Their No. 3 is a practice-squad holdover from last season, Seth Roberts. Their No. 4 is Andre Holmes, who was their No. 2 in ’14.

This season, the Raiders’ average per reception has increased to 11.3 yards from 9.5 yards in ’14. Holmes’ went from 14.7 yards to 16.8. It’s not solely a function of Cooper, but he’s the reason the Raiders’ receiving corps has gone from liability to asset.

“You’re always concerned about a guy that can beat you on any one play,” Capers said. “This guy’s made a lot of big plays.”

The Packers, in the meantime, have felt Nelson’s loss more than even they likely projected.

Going into the season, there was good reason to think the Packers might challenge the franchise scoring mark of 560 points, set in 2011. That’s the third-highest scoring season in NFL history.

They had their entire offense back after leading the NFL in scoring in 2014. With Davante Adams entering his second season as the No. 3 receiver and third-round pick Ty Montgomery a possible No. 4, this offense appeared to have plenty of passing-game weapons plus a running threat in Eddie Lacy that the ’11 team lacked.

When Nelson went down, you knew it was a big blow. But I still figured them to be a top-five offense. They haven’t been close to that.  They rank No. 12 in points and No. 18 in yards.

If last week’s improved tempo and production with Mike McCarthy back running the offense against the Dallas Cowboys is any indication, the play calling was one factor. Quarterback Aaron Rodgers bears some responsibility as well. As a premier player at the game’s most important position, he has to find a way to put up points even with a receiving corps he clearly doesn’t trust.

But Nelson’s absence has been more disruptive than I ever imagined. With Cobb neutralized by regular double teams, the inability of Davante Adams and Jones to get open as the season has gone on has been an eye opener.

The Packers took that risk with Jones when they immediately installed the 31-year-old as their No. 3 after the Giants cut him at the end of camp. Rodgers clearly was comfortable throwing to him upon his return, and Jones helped their offense early – he had four touchdowns in the first three games.

But as the season has gone on he has become a non-factor, and only lately have the Packers started mixing second-year pros Jared Abbrederis and to a lesser extent Jeff Janis into the rotation. Maybe neither would have improved enough with more playing time in games and practice early in the season to make a difference now, but we’ll never know because Jones took all those snaps.

Adams, on the other hand, has been one of the Packers’ great disappointments this season. He looked like an ascending player at the end of his rookie year, and by all accounts distinguished himself in offseason practices, which were mostly closed to media. But he has done little since returning from an ankle injury that cost him essentially four games early in the season.

Adams is second on the team in targets (73) but only No. 4 in receptions (38). His average per catch (9.3 yards) is low for a tight end, let alone a receiver, and he has only one touchdown.

He has OK size – almost identical to Cooper at 6-0 7/8 and 212 pounds – and an outstanding vertical jump (39 1/2 inches).  But he hasn’t played as big as that leaping ability would suggest, and he doesn’t play any faster than his 4.56-second 40, which is an average-at-best time for an NFL receiver.

Right now he looks like his confidence is shot. If it’s still too early to give up on him, it’s not too early to wonder if general manager Ted Thompson whiffed on his second-round pick last year.

So Nelson’s injury has done the opposite of Cooper’s addition to the Raiders. The cascade effect of his absence has exposed shortcomings in the rest of the Packers’ receiving corps.

Cobb now is facing the No. 1 cornerback and safety help over the top, instead of the single coverage from a No. 2 or No. 3 last year. Adams has moved up in the pecking order, and so has his cover man. And the Packers clearly don’t scare secondaries anymore.

“When the play would break down (Nelson) would convert his route, get up field and the quarterback could get the ball to him,” the AFC West scout said. “(Defenses) don’t feel threatened down the field against Green Bay (anymore).”

— pdougher@pressgazettemedia.com and follow him on Twitter @PeteDougherty.