When the smoke bomb flew from somewhere in the south stand and landed in the penalty area, Villarreal's striker Jonathan Pereira followed the standard procedure: he walked over to the canister and kicked it, sending it rolling towards the edge of the pitch, then turned to get on with the game. Nothing to see here and no time to waste. It was 11.42pm on Saturday night and there were just three minutes left.

Somehow Villarreal were losing 1-0 at home to Celta Vigo, slipping four points behind Athletic Bilbao in the chase for the final Champions League place, and Athletic were still to play the following night. The Yellow Submarine needed something and quick. But the plumes that rose around Pereira reached higher and wider than normal and then it started: the coughing and the choking and the crying. The smoke engulfed the stadium, thick and impenetrable, and not far away Celta goalkeeper Yoel suddenly felt like he was suffocating. Tears welled up in his eyes and his throat tightened. "It was like I was drowning. I couldn't breathe and I couldn't see properly," he admitted.

The Villarreal midfielder Tomas Pina was standing 20 metres away: "I started to cough and my eyes were burning." Something was wrong; this wasn't the typical bengala or smoke bomb, common in Spanish stadiums. This was tear gas. "Military issue," police said. Celta's team doctor called the players over to the touchline, shirts were pulled over mouths and noses and cold water was poured onto reddening eyes. Then the players disappeared down the tunnel, seeking safety away from the smoke.

"The stinging sensation was powerful," said Villarreal's captain, Bruno, "and we were worried because we also knew that we had friends and family in the stands." Somewhere up there, a father picked up his 10-year-old son, an asthma sufferer, and made for the exit as quickly as he could. An announcement over the loud speakers recommended that others do the same. Mostly it was calm and rational and actually quite impressive: 15,000 people were eventually evacuated in just eight minutes.

There was also something surreal about it at first, as if this just wasn't that much of a big deal. It couldn't be, could it? And yet the sensation of insecurity grew. The niece of the recently retired Javier Farinós dislocated an arm heading for the exit on the night when her uncle's ex-team-mates had run onto the pitch wearing t-shirts that said: "Gracias Fari".

"There were moments of anguish," Bruno said. Cameras showed club directors heading out, breathing through hankies. The ballboys collected up the balls and ran for the players' tunnel. In the stadium and at home, people wondered what was going on. The TV channel showing the game, whose powerless commentators were in a studio 430 kilometres away, did what it does and went to ads. Some reported that the game would be postponed, including Celta's Twitter account.

In the end, that wasn't necessary. Fifteen minutes passed. The sprinklers were turned on and players gulped down water and rinsed their eyes. The tear gas had hit at 11.42pm. At 11.56 the players were back out again, warming up. The fans weren't there. At midnight, the loud speakers announced that the game would restart in five minutes and fans could return. Most had gone. At 12.05am the game restarted in front of largely empty stands and at 12.08 Celta de Vigo scored the second.

Asked what the "experience" had been like afterwards, Villarreal's manager, Marcelino, stared ahead, his jaw clenched and his brow lowered. "Shit," he said. He continued: "There are human beings that do things that are impossible to understand. I think the best thing we can do is not even talk about it. The game is more important than some lunatic who's seeking attention."

He was right, of course, and there was much to talk about from the game. This was Celta's third win in four, with the other a 0-0 draw against Athletic Bilbao, and they are now just three points from a European place. For much of the season they've got less than they deserved; now they've started getting what they deserved. In fact, here they got even more than they deserved.

For Villarreal, it was a third defeat in four, their second in a row, after a run of three consecutive wins in which they scored five against Rayo, five against Real Sociedad and beat Almería 2-0. No one could understand how it happened. Bruno was superb again, Villarreal had 10 shots, Jérémy_Perbet missed two great chances, Marcelino rightly talked about "a crushing dominance" and Luis Enrique admitted that Celta had been fortunate.

But if Marcelino was right about that, if he was right when it came to not wanting to talk about some attention seeking lunatic, he was also wrong. It was inevitable that it was the tear gas that attracted the most attention. All the more so in a week in which the headlines had been dominated by the lighter thrown at Cristiano Ronaldo's head by an Atlético Madrid fan. "Where will we end up?" asked Marca's cover on Sunday morning.

"This is more dangerous [than the lighter thrown at Ronaldo] and it is controllable," said Javier Tebas, the president of the league. "Measures have to be taken, to make sure this doesn't happen again. The problem is that Villarreal's security failed." Villarreal insist that they cannot frisk every single fan coming into the stadium, while Luis Enrique was swift to differentiate between one isolated incident and a entire fan base, but the consequences could be significant.

Depending on whether the disciplinary committee judges what happened to have been "grave", El Madrigal could be closed for anything from one game to two months. Villarreal remain hopeful that it will not be closed at all. After the game, their president, Fernando Roig, gave a press conference to condemn what had happened. Villarreal is a club with virtually no history of trouble, that has no ultras, and Roig was at a loss to explain events.

"I can't make head nor tail of it. The ball wasn't there, there was no one moaning at the referee, or anyone else, no tension," he said. "Some gutless hooligan from outside the club has tried to damage Villarreal." But who? Villarreal are not only a club without ultras, they're a club that's almost universally popular, and one that doesn't even really have significant rivals.

Roig also publicly rejected suggestions that it could have been someone who has it in for him personally. Privately, though, that hypothesis is not being ruled out. One thing is for sure: this was a premeditated attack. You don't just accidentally turn up at a football stadium with a tear gas canister in your pocket, get wound up a bit and chuck it on the pitch.

The canister is basically the same set up as a grenade, with a pin, a release handle and a detonator, of the type used by the military and riot police, although Spain's national police force say it is not like the ones they use. It cannot be bought legally.

Initially, there were suggestions that it had been fired from a gun by a man wearing a balaclava who had sneaked into the stadium in the final 10 minutes when the turnstiles are opened for supporters departing the ground and then made a run for it. Now, police believe that he had been in the stadium for the whole game and footage shows that he was not disguised.

The images are not clear enough to identify him yet but he was around 30 years old and 1.70m tall. Standing in one of the gangways, after throwing the canister by hand, he put on the coat he had hung over his arm and walked slowly out of the stadium, literally disappearing in a puff of smoke. He didn't wait to see the trouble he'd caused.

Talking points

* Sevilla versus Valencia should have been a great game. Instead, it was a strange, sometimes surreal shambles of a match in which everyone shot but no one could shoot on target, in which there was loads of space but no one to take advantage of it and in which Sevilla seemed to be playing with a sweeper 27 miles behind everyone else and employing a revolutionary no right-back formation, while Denis Cheryshev came on in the 59th minute, got booked in the 69th and was sent off in the 92nd, for getting fouled in the area.

It also had a dreadful referee, you see. Álvarez Izquierdo gave a penalty that was less of a penalty than the four or five he didn't give. Still Sevilla didn't score. Ivan Rakitic, easily their best player this season, missed his third penalty of the campaign, the first Sevilla player in 23 years to do so. Or more to the point, Diego Alves saved it, just as he has saved penalties from Lionel Messi, Cristiano Ronaldo, Fredi Kanouté, and Fernando Llorente. On average 75% of penalties are scored but, according to football statistician Mr Chip, Alves has faced 28 and let in just 14. He has saved 12 of them, a whopping 43%.

* "The history books will show that Espanyol were the first [away] team to win at [the new] San Mamés", beamed Javier Aguirre after his side's 2-1 win in Bilbao took them level with the European places. Aguirre's nickname? El Vasco. The Basque.

* After two minutes, Barcelona scored. After three minutes, Atlético Madrid scored. After four minutes, Atlético scored again. And after five minutes Real Madrid scored. They're still level at the top of the table on 60 points each. Valladolid, Rayo, and Getafe, their opponents, continue to be in trouble. Messi and Neymar scored lovely goals for Barcelona, Diego Costa lobbed one in for Atlético, making it 21 for the season, and Jesé curled home a beauty for Madrid. "A goal that only six or seven players in the league could score," the former Atlético Madrid striker Kiko said.

* The most entertaining match of the weekend was probably Ramos versus the ref. Sergio Ramos is on four yellow cards and he decided that he quite fancied being on five yellow cards. That way he would get a game suspension, sit out against Elche and come back against Atlético with the slate wiped clean. So he went looking for the fifth in the final 15 minutes against Getafe. There was just one problem with the plan: the referee Pérez Montero was wise to it. Ramos committed five fouls in the game and those were the ones that were given; there were as many again that weren't. However hard Ramos tried -- and he tried pretty hard, handballing and kicking and pushing and protesting and flying in - Pérez Montero stubbornly, and comically, refused to pull out the card. When the whistle went, the best man had won and covering his mouth to avoid the lip-readers, close to breaking into a giggle, Ramos could only offer his hand and his congratulations. Well played.

Results: Elche 0-0 Osasuna, Atlético Madrid 3-0 Real Valladolid, Levante 1-0 Almería, Barcelona 6-0 Rayo Vallecano, Villarreal 0-2 Celta Vigo, Granada 1-0 Real Betis, Getafe 0-3 Real Madrid, Athletic Bilbao 1-2 Espanyol, Sevilla 0-0 Valencia. Monday: Málaga-Real Sociedad.

Latest La Liga table here