Two years ago, the acquisition of Randy Moss was supposed to herald a return to the high-flying, pass-heavy offenses of the Oakland Raiders’ glory days. But it didn’t quite work out that way.The 0–4 Raiders are now the NFL’s worst team, their struggles exemplified by Moss’s actions off the field and inaction on the field.

After four games, Moss has just 12 catches for 136 yards and two touchdowns. Although he never gained fewer than 1,200 yards in his first six seasons, he struggled with injuries in his final year with the Vikings and barely topped 1,000 yards after his trade to Oakland last year. Now, in his ninth season, he is on pace to gain a whopping 544 yards.

Only once has Moss finished a year averaging fewer than 14 yards per catch; this season, his average is just 11.3 yards. Moss doesn’t even lead his team in receiving yards — that honor goes to Ronald Curry.

Just a year and a half into his time with the Raiders, Moss once again is making noise about wanting a trade out of town. “If they’re not going to use me right,” he said in a radio interview last week, “then trade me or get rid of me at the end of the season or during the season. It might be good for me to go elsewhere.”

Moss isn’t the only one who believes he could return to his glory days with a different team. The popular assumption is that Moss could be one of the league’s top receivers if he only had better talent around him.

Oakland has started four quarterbacks since it acquired Moss, each one worse than the one before him. The current Oakland quarterback, 2005 third-round pick Andrew Walter, had not started an NFL game until two weeks ago. The subpar Raiders quarterbacks are made even worse by the blocking (or lack of thereof) from the league’s worst offensive line.

But it would be a mistake automatically to assume that Moss, now 29, could just turn his talent on again after three off years. For evidence, look at the wide receivers since 1978 who have followed a career path similar to Moss’s over the last three seasons: a spectacular year at 26 or 27, followed by a down year, and then a slight rebound. Using a system of similarity scores developed at Football Outsiders, we can see that most of these receivers were not able to turn their careers around.

The receiver most similar to Moss in numbers is also fairly similar in circumstance. John Jefferson was a spectacularly gifted athlete who had at least 1,000 yards and 10 touchdowns in each of his first three seasons, 1978–80, playing for the powerful offense of the San Diego Chargers. Upset with his contract, Jefferson forced a trade to Green Bay, one of the league’s worst teams. And like Moss in Oakland, Jefferson was never the same, struggling with injuries and ineffectiveness. He was out of the NFL by age 30.

Jefferson is not an isolated case. The five most similar receivers after Jefferson are Mike Quick, Antonio Freeman, Lynn Swann, Carl Pickens, and Dwight Clark.

Like Moss, each of these receivers was immensely talented in his youth. Each had a three-year span similar to Moss’s past three seasons. From that point on, not a single one had a season with more than 820 receiving yards. All six were out of the NFL by age 32, including Hall of Famer Swann. (After the top six, there are some similar receivers who did recover from a midcareer decline, including Isaac Bruce and Terance Mathis.)

The list of comparable players is even worse if we project Moss’s current numbers over 16 games and then look at 2004–06. Of the 20 wide receivers with the most similar career paths, only two (Mark Carrier and Brett Perriman) ever had even 800 yards in a season again.

Each of these receivers played under different conditions — different quarterbacks, different offensive lines, different injuries — and their fading careers are no guarantee that Moss won’t return to greatness. But the numerical evidence is backed up by what we know of Moss’s personality.

A professional athlete’s career generally presents a tug-of-war between two trends. His athletic talent will decline with age, but his knowledge of technique and the intricacies of strategy will improve with experience. A player who has spent his early years as a student of the game can often extend his career, even once his body begins to slow down significantly, usually around age 30.

But Moss has always been a player who depends on his athletic gifts rather than technique. He is well-known for sometimes failing to block on running plays, or running extremely lazy routes on pass plays that are not designed specifically to go to him. His favorite routes have always been the most simple: the go route, which requires him just to outrun defenders, and the jump ball in the end zone, taking advantage of his size.

A team that trades for Moss must understand that his athletic gifts are deteriorating. His height will never disappear, but his speed will fade. In order to stay effective, he will need to dedicate himself to the game, eliminating his sloppy habits and sometimes poor fundamentals. Does someone who tells a radio host, “I’m not even too concerned with football right now … I’m just loving life” sound like a player who is ready to make that trade worthwhile?

Mr. Schatz is the editor in chief of FootballOutsiders.com.