Doing a project like this, you run into a lot of what-if scenarios; players whose careers were cut short or derailed by circumstances beyond their control.

Usually, that means injuries. Bobby Orr is one guy I singled out, as is Gale Sayers, but at least they established their greatness. Bo Jackson never got going. Don Mattingly went from sure Hall of Famer to journeyman first baseman.

Military service intrudes, too. Ted Williams is the most famous example, but dozens (maybe hundreds) of athletes had their careers interrupted, diminished or ended by wartime service. Even into the ’50s, guys like Willie Mays and Elgin Baylor had their development interrupted by the call to a different uniform.

And, of course, entire generations of black athletes were denied the chance to even step on the field.

And then there’s Steve Young. I can’t think of another star quarterback that had a comparable road to greatness. Others have faced bigger obstacles, or harder luck. But nobody else has had a career that was quite as weird.

He came out of Bringham Young a star prospect, and signed with the ill-fated USFL for  $40 million, of which he would only see a fraction. After two years, the league collapsed and he joined the Tampa Bay Buccaneers, which is a little like asking a race car driver to win the Daytona 500 in your mom’s Corolla.

After two more years the Bucs gave up on him (because, of course, Steve Young was the problem there), and traded Young to the 49ers, who already had future Hall of Famer Joe Montana at quarterback. On any other team (except the Bucs, obviously), Young would have been the starter, but in San Francisco, he would be Montana’s backup for four seasons.

An injury to Montana in the 1990 playoffs meant that Young finally got his shot. Montana would miss almost two complete seasons, and by the time he was ready to play again, it was obvious that Young was the Niners’ future at quarterback. After a brief controversy ahead of the 1993 season, the veteran star Montana was traded to Kansas City.

In San Francisco, Young continued to excel, culminating in a Super Bowl win after the 1994 season. But his time was short; injuries would keep him increasingly off the field and three games into the 1999 season, at age 37, he suffered the final injury, a concussion against the Cardinals that ended his career.

In between, he put together an eight-year run in which, in my estimation, he played the quarterback position at a higher level than anyone has before or since. No other signal-caller combined the ability to run and throw as seamlessly, or to such devastating effect. Other running quarterbacks (such as Randall Cunningham or Michael Vick) use their legs to get out of trouble, or as a backup when they don’t see a good passing option. Some scramblers, like Montana, would run to buy time and find the killer pass. Young could do that, too, but he also used his running skills to attack the defense.

The best example: In a 1994 game against the Cowboys, he ran a series of bootlegs against Dallas pass-rush ace Charles Haley, taking advantage of Haley’s aggressiveness and running into the open field behind him. For the rematch in the playoffs, the Cowboys vowed to contain the bootlegs; instead the 49ers called designed draws up the middle, leading to 47 yards and a touchdown. Then, in the Super Bowl against the Chargers, Young threw six touchdown passes, breaking Montana’s record, and ran for another one. His versatility was unparalleled.

Among modern QB’s, I rank him behind only Dan Marino and Peyton Manning, with Tom Brady likely on the way. All three of them played substantially more games than Young. Where would he rank with a real career, one not stalled on mismanaged teams or sitting behind a living legend? It’s a fascinating question, possibly the most fascinating I’ve come across.