Super Bowls are supposed to be about the players. But not edition XLVII of America's gaudiest sporting pageant – or at least not until the San Francisco 49ers and Baltimore Ravens actually kick off in the New Orleans Superdome, a few moments after 11.30pm British time tomorrow. This time it's been a tale of two coaches.
In American football, perhaps more than any other sport, coaching is a family business. Maybe it's a matter of genes; maybe, in so fiendishly complicated a sport, growing up amid the game from early childhood gives you a special head for strategy. Whatever the reason, down through the ages of the National Football League, coaches have begotten coaches.
But even the NFL has never seen any- thing quite like the Harbaughs. Jim Harbaugh and John Harbaugh are brothers, sired by Jack Harbaugh, in his time one of the top coaches in US college football. Jim, born in December 1963 and the younger of the pair by 15 months, is in charge of the San Francisco 49ers.
John is his opposite number at the Baltimore Ravens. As children they used to share a bedroom. Now not only are they the first pair of brothers to become NFL head coaches. They now find themselves on opposite sides in the league's marquee game. And one of two ferociously competitive siblings will finish the night a loser.
In their playing days Jim, who spent 14 seasons as a quarterback in the NFL, was indubitably the better athlete. John never made it beyond college level as a player, honing his trade instead as a coordinator and defensive coach for the Philadelphia Eagles, before moving to Baltimore. There he made the play-offs in each of his five seasons in charge. In the one head-to-head match-up, on Thanksgiving Day 2011, John Harbaugh's Ravens prevailed in a dour defensive match-up, 16-6.
The brothers both own explosive tempers – but give John the narrow edge here (though no NFL coach is a sweet-tongued angel as he prowls the touchline during the game.) One former NFL official responsible for referees drew the distinction this way: "he [Jim] goes quickly off the deep end, while John seems to be more constantly off the deep end."
And both of them are ready to gamble, as they proved in 2012. In Baltimore, John changed the team's offensive co-ordinator three-quarters of the way through the season, sparking a resurgence that resulted in the Ravens averaging more than 427 yards and 30 points over their three play-off games to reach the Super Bowl.
In San Francisco, Jim Harbaugh switched quarterbacks, with no less wondrous results. Colin Kaepernick started 2012 as the back-up to Alex Smith. In early November Smith was injured and Kaepernick, in just his second season, took over as starter. In his first game in the play-offs, he led the 49ers to a 45-31 victory over the Green Bay Packers – who had been tipped by many to go all the way – in the process breaking an NFL single game record for a quarterback, with 181 rushing yards.
And tomorrow evening, Kaepernick, in just his 10th game as starter, and his opposite number Joe Flacco of the Ravens, will definitely take centre stage. The "HarBowl" will finally become the Super Bowl, in which the outcome will ultimately be decided not by the coaches and the plays they call, but by the ability of the teams on the field to execute those plays.
Even without the saga of the touchline frères ennemis, this would have been a Super Bowl to remember, what with 30-second TV spots costing a record $3.8m (£2.4m) apiece – complete now with ads to trail the ads – as well as rumours, happily unfounded, of a national shortage of chicken wings, the couch potato's traditional snack.
A small pall was cast over proceedings by a warning from President Obama in a magazine interview that the NFL might have to change its rules to reduce the violence in the game and the risk of serious head injuries, even at the risk of making the sport less exciting. But quite possibly, this will be the most watched programme ever on US television.
Recent Super Bowls have been nail-biting affairs, with four of the last five won and lost on the final drive. But this one could be a whole game to remember, between two teams once best known for their defensive prowess, but which have suddenly broken loose on offense as well.
The Las Vegas oddsmakers have installed San Francisco as marginal favourites. But being given that edge merely underlines that after two impressive underdog victories in the play-offs – first against the Denver Broncos, many experts' pick to win it all, and then over Tom Brady and the New England Patriots – only a fool would write off the Ravens.
As always, the focus will be on the quarterbacks. Will nerves get the better of Kaepernick, forcing a crucial mistake late on? Or, in the perverse way of these things, will inexperience breed fearlessness? Having featured in the play-offs for five straight years, Flacco is battle-hardened. On the other hand he has rarely distinguished himself in this setting. The pressure to do so now could be crushing. Or again, maybe Baltimore, with legendary middle linebacker Ray Lewis playing in his last game, truly are the Team of Destiny. On Super Bowl Eve, just one thing is certain. Come Monday, there will be one elated Harbaugh brother. But which?
Family face-offs: Brothers at play
Eli and Peyton Manning
If people were told a couple of years ago that two brothers would meet in a Super Bowl, most would have guessed it would be the Mannings. In 2006, the pair became the first brothers to start against each other as quarterbacks and both have won Super Bowl rings, Eli twice.
Michael and Ralf Schumacher
The Germans are the only brothers to have both won F1 races and were also the first pair to finish first and second in the same race.
Dean and David Holdsworth
In 2010, David and Dean became the first twins to face each other as football managers. Dean's Newport County beat David's Mansfield Town 1-0.