"Away from home, our fans are fantastic," former Manchester United captain Roy Keane once observed. "I'd call them the hardcore fans. But, at home, they have a few drinks and probably the prawn sandwiches, and they don't realise what's going on out on the pitch."
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All clubs have small sections of supporters who are nothing other than a source of shame. There are those who enjoy singing songs about plane crashes and stadium disasters, while other ignoramuses prefer to racially abuse opposition players.
When it comes to actually turning on their own, though, there are few worse fans than the select few that get to go to Real Madrid games every week and feel perfectly entitled whistling and booing the likes of Cristiano Ronaldo and Zinedine Zidane. They made their voices heard again at the Santiago Bernabeu on Wednesday night, with los Blancos a man and two goals down to Las Palmas after just over an hour of play.
As ever, Ronaldo, Real's all-time record goalscorer, was doing his utmost to drag his side back into a game that the hosts needed to win to reclaim top spot from bitter rivals Barcelona. However, when the Portuguese uncharacteristically miscontrolled the ball, allowing it to run out over the touchline, some Madrid fans voiced their disapproval with Ronaldo.
Then, just seconds later, Zidane bore the brunt of the boo boys' mounting frustration for having the temerity to withdraw Isco. The midfielder had opened the scoring in the Spanish capital yet had disappeared in the second half. His substitution was justified yet the move was greeted with howls of derision.
Talk about short memories! Even if one overlooks the fact that Zidane won the Champions League for Real both as a player and a coach, as well as overseeing a 40-game unbeaten run between April and January, it was the Frenchman who, only four days previously, had masterminded a remarkable comeback at Villarreal with his second-half substitutions (Isco and Alvaro Morata).
Furthermore, for any Real fan to criticise Ronaldo is just ludicrous, given the €94 million that Madrid paid Manchester United for his services has long since been proven a bargain. He has won the Ballon d'Or three times since moving to the Spanish capital, lifted two Champions League trophies and scored a frankly ridiculous 389 times in 379 games in all competitions.
Of course, no player or coach should be exempt from criticism just because of past glories - see Arsene Wenger at Arsenal - but Zidane and Ronaldo's successes should still be fresh in the memory.
As former Real No.1 Iker Casillas recently said of the jeers, "As a Madridista, sometimes you don't understand how it can happen. Last year, Madrid were European champions. A few months ago, they were world champions! [Ronaldo] has just won the trophy as the world's best player!"
Furthermore, it is not as if Ronaldo has suddenly stopped fighting. It was he who ultimately salvaged a point for Madrid against Las Palmas, by converting a penalty and then heading home a last-gasp equaliser. There was no preening, no self-indulgent celebration either. After both goals, Ronaldo quickly tried to recover the ball from the net in order to restart the game as quickly as possible.
And yet some Madrid fans feel he doesn't do enough! It's embarrassing and those responsible should be ashamed of themselves.
However, this is nothing new. Ronaldo has been booed several times before - and he is not the only one. Karim Benzema has been repeatedly targeted, while Gareth Bale was heckled while he was still trying to settle in Spain and fight his way back to full fitness after several injury issues.
How exactly do some Madrid fans feel they are helping their players? The staggering thing is, though, that there is now an attitude of acceptance among the longer serving members of the Real squad. Sergio Ramos, for example, sees no reason why Ronaldo should be exempt from the boo boys' backlash.
"I can understand why [the fans] whistle Cristiano," the centre-half admitted. "Why not? They have also whistled me. They whistled Manolo Sanchis, [Jose Antonio] Camacho, [the Brazilian] Ronaldo, [Zinedine] Zidane. The fans have whistled everyone."
Only, that's not true. It hasn't always been like this. Legendary Real striker Hugo Sanchez recently claimed that he never had to put up with flak from his own fans.
"I suffered many difficult situations, lots of insults - but playing away from home," the Mexican pointed out. "At the Bernabeu, you expect support and affection to lift you.
"It is something strange what is happening with Cristiano. Ronaldo, season after season, is the leader and goalscorer who gets the team out of difficult moments.
"We must keep respecting him, supporting him, and helping him."
Unfortunately, that plea is likely to fall on deaf ears. As has been demonstrated time and time again at the Bernabeu, empty vessels make the most noise and some stupid supporters are more interested in jeering their own players rather than cheering them.