Stud marks were adorned to the chest of Barcelona's Jose Escola as he left the Les Cort's pitch in 1943. They had been inflicted by Real Madrid's Jose Maria Querejeta and were veritable evidence to the rivalry that existed before, during and since that game.
That game was the semifinal first leg of the King's Cup—renamed the Generalisimo Cup by Franco at the time—and was won by the Catalans 3-0.
Phil Ball notes in his book "Morbo" that there was an inevitability that Madrid would win the return leg in the Spanish capital. They did, 11-1.
The two legs of this cup tie featured many aspects which have remained underlying themes which have followed the El Clasico rivalry from the early days of the 20th century through to the present day.
Immediate thoughts of Querejeta's boot being stuck into Escola draw parallels to Pepe's stamp on Lionel Messi in the 2012 Copa del Rey, but there is, of course, much more to the rivalry than the current spats which present themselves on more than two occasions each season.
Fueled by the press—Marca and AS in Madrid and Sport and Mundo Deportivo in Barcelona—the two sets of fans are fed information by media sources who have no qualms in displaying their allegiances, quite the opposite.
Ahead of Luis Figo's return to Barcelona in 2000—he'd left them for Real Madrid—Marca ran the headline "Figo: Te van a calentar la oreja" (they'll make your ears burn).
They did, and not just on this occasion, but every time he ventured to Camp Nou. His first visit saw Barca fans waving thousands of fake 5,000 peseta notes, calling him a "pesetero" (money grabber).
Two years later the hurt will still felt in Catalunya, a suckling pig and a full bottle of whisky were famously thrown at him as he tried to take a corner.
Luis Enrique moved the other way. Real Madrid to Barcelona in 1997. Marca labelled him a "Traitor" and added "we know what happens to them." Enrique scored on his return to the Bernabeu, and his relationship with Los Blancos since can perhaps be described as untenable.
And then there's the whole Alfredo Di Stefano transfer affair of the early '50s, best read about here.
Press speculation, player brutality and fan warfare though, does not make the rivalry between the two any more sincere than some of the world's other rivalries. What El Clasico does possess which differentiates it is underlying political issue which can be aligned with Spain's 20th century history.
This season “Independencia” chants—a political reference to Catalunya’s bid for secession—after 17 minutes and 14 seconds of each half (1714 was the last time they were independent) have been at every home game, none louder though than when Madrid visited in La Liga in October.
Those political feelings even festered in La Segunda this season, evident—along with all the other aspects of the rivalry—at the Mini Clasico between Barcelona B and Real Madrid Castilla at the Mini Estadi last month.
To go into the history of Barcelona in the General Franco years, the death of Josep Sunol and more is much more complicated than merely a rivalry. A brief summary can be found here.
Through the media and through the fans, through the players and through the politics, Real Madrid and Barcelona enjoy a distinct rivalry that at very least makes it among the greatest in sport.