If championships in pro football were decided by the players with the stats that matter most in fantasy football, Michael Vick would be a great quarterback. If championships were decided by the quarterbacks with the greatest athletic ability, Vick would be the greatest quarterback who ever lived.

Last season, Vick ran and passed for 3,009 yards and 21 touchdowns; his totals the year before were 3,215 yards and 17 TDs.This year’s stats look to be equal or better: After three games, he’s projected to have more than 3,200 yards of total offense by season’s end.

That’s great if your primary interest is fantasy football, not so great if you’re an Atlanta Falcons fan. Despite the Falcons’ winning record through the first three weeks of the season and the goose bumps TV executives get when they think about the ratings Vick could pull in if the Falcons made the playoffs, it’s about time to wonder whether Vick will ever fulfill his potential or, maybe more to the point, if football is the sport his potential is really suited for.

Vick could probably win a footrace with any quarterback, most running backs, and even many wide receivers in the league. Most likely, he’s stronger pound-for-pound than just about anyone in the NFL who is given the unfortunate job of trying to tackle him.The problem is that in football, great athletic talent in and of itself has never been all that important, at least not for quarterbacks. Bart Starr, Terry Bradshaw, and Joe Montana wouldn’t have finished very high in a decathlon or triathlon, but they won 13 championships among them.

In a contest of pure ability, Vick could have whipped all three of them. He turned 26 in June; at that age, Starr and Bradshaw were headed for their first championship games and Montana already had a ring. Vick’s ring clock is ticking. It’s ticking even faster for him than it has for other Hall of Fame quarterbacks because any day now, Vick is going to find that he’s lost a step and some hungry young linebacker who wants a highlight on ESPN can now catch up to him a split-second before he makes it out of bounds.

This is Vick’s sixth season; the closest he has come to winning anything substantial is second-round playoff losses in 2002 and 2004. He is almost certainly what most football commentators call him: the most exciting player in the league. But that is largely because he is so wildly inconsistent and, therefore, unpredictable. The Falcons’s offensive coordinator, Greg Knapp, has come under much fire for his inability to produce an effective offense with a talent like Vick to lead it. But how can you be a good coordinator with a quarterback who wants only to improvise?

His 2005 NFL passer rating was just 73.1, good for 25th in the league, and his career rating of 76.1 is considerably less than mediocre. If you don’t understand or trust the NFL’s passer rating, go with simple stats: Vick has played 63 NFL games and has completed less than 55% of his passes, which means he misses nearly as often as he connects. He is only 20% more likely to throw a touchdown pass than an interception, and in the all-important stat of yards per throw, he’s at just 6.7, which has put him in the bottom half of the league’s passers since 2001.

His postseason passing stats are even less impressive: in four games, he has averaged a dismal 5.9 yards per throw and has matched three touchdowns with three pickoffs.

On the other side of the ledger, Vick might be the best running quarterback the NFL has ever seen. He has already rushed for more than 3,000 yards and a sensational 7.0 average. Just to compare, the yards per rush averages of Randall Cunningham and SteveYoung, regarded as the best running quarterbacks of the previous generation, were 6.4 and 5.9, respectively. In the NFL, though, running is the smaller side of the ledger.

No quarterback whose primary talent was running has ever won a championship in the modern NFL. For one thing, what all those gaudy running stats don’t show you are the big losses a quarterback gets dropped for when he scrambles from one side of the field to another looking for an opening. (It often seems as if Vick has to run 20 or even 30 yards just to gain 10 from scrimmage.) Some of those losses go under the “Pass Attempt” column and thus don’t show up in the rushing stats. They also don’t show you all the extra holding calls incurred by offensive linemen who have to hold their blocks two or three times longer than they would on straight drop-back passes. Above all, they don’t show you how weary your offensive linemen can get late in the game.

Smart quarterbacks usually don’t require but a couple of seasons to understand that the main purpose of all that speed and mobility is to evade pass rushers and allow your receivers time to break free of coverage. Steve Young, a quarterback whose talents were eerily similar to Vick’s, didn’t really understand this until he came under the tutelage of Bill Walsh at San Francisco.Donovan Mc-Nabb seems to have finally figured it out and may be headed for the best season of his career, as well as the likelihood of a productive career beyond the age of 30. Vick is still scrambling, and, in his oft-repeated words, “trying to make something happen.”

The only thing that happened in Monday night’s humiliating 23–3 loss to New Orleans was a textbook lesson from the Saints’ defense in how to contain Vick. Instead of rushing him wide — generally a futile tactic, as the Atlanta blockers simply push the pass rusher farther out to the flanks, enabling Vick to take off up the middle — the Saints came with a strong inside rush that included several blitz packages. This forced Vick on nearly every play to roll either to his right or left, which not only took away half of the field to throw to, but to run to as well. The result was just 12 completions in 31 tries for only 137 yards. He did rush for 57 yards on six tries, but much of that was lost in five sacks that negated 25 yards.

In the NFL, quarterbacks have a short shelf life, and running quarterbacks have an even shorter one. Michael Vick has been granted a dispensation from his fans for most of the criticism pro quarterbacks are subject to, but the time is fast passing when people are going to be judging Vick by his potential rather than what he’s done. And what’s he done since he left college is practically nothing.

Mr. Barra is the author, most recently, of “The Last Coach: A Life of Paul ‘Bear’ Bryant.”