To the vast majority of mankind who do not play top-level professional sport for an extremely lucrative but stressful living, the experience is unimaginable: the sight and sound of a stadium filled with 70,000 people baying for your blood. Last season however, and more than once, that fate befell Alex Smith, quarterback of the San Francisco 49ers, as what was once one of the NFL's most glittering franchises lived out yet another dreadful year.
But last weekend thunderous cheers, not boos, exploded from Candlestick Park, perched on the edge of San Francisco Bay. The 49ers were back in the play-offs for the first time in almost a decade. And Smith, so recently reviled, had just led them to victory in one of the greatest post-season games in League history. Now, if they defeat the New York Giants tomorrow in the NFC championship game, they will be in the Super Bowl itself. And the key to this amazing transformation of a team and quarterback? Basically, it's been a new head coach.
When Smith was drafted by the 49ers as the first overall pick in 2005 – a reward for the team with the worst record the previous year, a fact that of itself explains the depths to which Joe Montana's old franchise had sunk – the sky seemed the limit for him. It didn't work out that way.
His first year was passable, but as the team floundered, there followed a succession of head coaches and offensive co-ordinators (six of the latter in six years), each bringing a new playing style for a quarterback to learn.
The glamour culture of the NFL dictates that when things go well, the quarterback is hailed as miracle-maker. But when they do not, then he must take the blame. And thus it was with Smith.
He wasn't a leader, they said. He couldn't make the big plays, they said. He turned the ball over, they said. He got injured too easily, they said. The 49ers flopped again in 2010, with a 6-10 record, and Smith was a free agent eligible to move to another team and put an end to his miseries in San Francisco.
That indeed was what his parents urged him to do, and his departure looked a done deal. But then Jim Harbaugh arrived as head coach from Stanford University, where he had run the football programme since 2006, bringing with him Greg Roman as offensive co-ordinator. He and Smith met, and hit it off.
The quarterback decided to give it one more try in San Francisco, and signed a single-year $5m deal – a fortune anywhere else, but a relative pittance for a starting NFL quarterback. "You could see how much he wanted it," Roman said this week, "he had been through so much here. But he didn't want to turn and run, he wanted to stay and fight."
Smith's 2011 regular-season figures were better, but they were far from fantastic: he threw for 3,144 yards, on 445 pass attempts that yielded 17 touchdowns. His interceptions were down, however, and a team built on its defence simply functioned better. The 49ers were supposed to be rebuilding, but astounded everyone with a 13-3 record, the best in the NFC.
Then came that game against the New Orleans Saints in the divisional play-offs. The 49ers won 36-32 in an epic confrontation where the lead changed hands four times in the last four minutes. In that brief period, Smith and his Saints opposite number Drew Brees traded two touchdowns each. For Brees – who had just come off a stupendous regular season, in which he threw for 5,476 yards to break the great Miami Dolphins quarterback Dan Marino's record that had stood since 1984 – that was standard operating procedure. But not for Smith, with his barely restored reputation, and as a game manager more than a game winner.
However, Smith produced a display that kindled memories of Montana. His second touchdown came at a point when a field goal, all but certain, would have tied the game, 32-32. Instead, with nine seconds left on the clock, Smith threaded a 14-yard pass to tight end Vernon Davis for the winning score.
"Alex is a changed guy now, he's a championship quarterback," says Steve Young, Montana's successor, who led the 49ers to the last of their five Super Bowls in 1994. "For the first time in his life, he's been given a platform. He does not know how good he is because he hasn't been given the platform before. Now he has it and you just have to sit back and revel with him."
But much of the credit also goes the erstwhile Stanford man, Jim Harbaugh. American college football is a multi-billion dollar national institution followed, if anything, even more passionately than the NFL. Harbaugh's immortal moment came in 2007, when Stanford beat the mighty Trojans, the University of Southern California, in arguably the greatest upset in modern college football history.
Few college coaches easily make the transition to the pro game. Harbaugh, however, did, with his patented combination of enthusiasm and confidence that transmitted to the players, Smith included.
"It wasn't his enthusiasm as much as his confidence," Alex Fletcher, one of Harbaugh's old Stanford charges, told The San Francisco Chronicle recently. "He just reeked of confidence. I don't think he'll ever lose at anything in his life. In 2007, we had no business being on the field against USC. He willed us to victory."
That triumph, in which Stanford never led until their final score with 45 seconds to go, bore all the hallmarks of Harbaugh's 14 years as an NFL quarterback with four teams, when he was known as "Captain Comeback" for his late-game heroics. The knack seems to be rubbing off on Smith, if three regular season come-from-behind victories and the unforgettable New Orleans game are anything to go by.
And if Smith does take the 49ers to the Super Bowl, Jim Harbaugh could make family history of his own. Tomorrow's other game, for the AFC championship, pits the New England Patriots against the Baltimore Ravens. The Ravens are coached by one John Harbaugh. If they prevail, the Super Bowl for the very first time will feature a pair of brothers as opposing head coaches. And if that happens, no one will be booing Alex Smith.