First Minister Carwyn Jones and UKIP leader Nigel Farage have clashed over the fate of the steel industry in a head-to-head debate on the UK's future within the European Union.
Mr Jones said leaving the EU would have "devastating consequences" for Wales, and asked what Mr Farage had done to help steel in his role as a Euro MP.
Mr Farage claimed membership of the EU had left the first minister "impotent".
He argued the UK would have more control of its economy outside the EU.
The UKIP leader opened the debate in Cardiff on Monday by asking if the UK wanted to "regain our independence as a nation state" or if it was happy to be a "subordinate member of the club".
Mr Farage claimed it was "scaremongering" to say trade would cease and jobs would be lost upon a British exit from the EU.
The first minister replied by saying membership of the UK and EU was vital to Welsh prosperity.
Claiming 200,000 jobs in Wales relied on EU trade, Mr Jones said "pulling up the drawbridge" would have "devastating consequences".
Focusing on the fate of steel, the first minister said the industry's problems were "nothing to do with the EU".
A glut of steel on the world market, the strong pound and high energy costs were hurting the industry, he said.
Mr Jones said he met Tata Steel bosses in December, adding: "Not once did they mention the European Union as being some kind of obstacle."
Mr Farage responded by claiming British politicians in Wales and Westminster had been unable to protect the steel industry from cheap Chinese exports.
"You didn't do it, not because you don't want to, because you haven't got the power to do it because we've given that away to Brussels," he said.
Analysis by Nick Servini, BBC Wales political editor
If the EU referendum campaign is going to be anything like this, it's going to be a lively affair.
It was breathless stuff - within minutes both men were trading insults.
And perhaps surprisingly it was jobs and the economy - not immigration - that dominated.
At times it was a tough night for the first minister with Nigel Farage bossing big chunks of the debate.
Carwyn Jones based his claims on the dangers of taking a risk - in other words, better the devil you know.
Nigel Farage's rhetoric was based around the need to reclaim control of our borders and our laws.
On the issue of immigration, Mr Farage said "the biggest benefit" of leaving the EU would be the UK's ability to set up an Australian-style points system to accept immigrants based on their skills, lack of criminal convictions and ability to speak English.
However, Mr Jones dismissed the suggestion that EU membership had "anything to do" with immigration, saying if the UK was not a member, France would simply allow refugees camped at Calais to pass through.
"Would it be in our interest to turn our backs on our European partners, or isn't it better to work together to find a European solution to what is a European challenge," he asked.
The first minister also attacked the UKIP leader's record as a Euro-MP, saying he had only attended one out of 42 meetings of a fisheries committee in the European Parliament.
"The reality is you don't stand up for Britain," he told Mr Farage.
In reply, the UKIP leader said: "If I spent every living moment there I wouldn't have even been allowed to debate or vote on the issues that affect fisheries - the parliament hasn't got that power."
Eluned Parrott, Welsh Liberal Democrat spokesperson on Europe, said that "neither person came out of this shouting match particularly well", claiming hers was the only UK party united in favour of EU membership.
"Carwyn Jones was right to be arguing the importance of the UK remaining in the EU," she said.
"Yet, his views are in stark contrast to his party in London, where [Labour leader] Jeremy Corbyn remains ambivalent on this major issue."
Plaid Cymru AM Elin Jones was critical of Mr Jones, tweeting: "Well, for the case for Wales staying in EU, that was a set-back. Mustn't be repeated. #IWADebate."
Before the debate, a spokesman for the Welsh Conservatives dismissed the event as having the feel of a "rather gaudy PR spectacle", saying Mr Jones had failed to invite rival party leaders to similar debates about Welsh issues under his control.
A referendum on whether the UK should remain within the EU or leave is set to be held before the end of 2017.
On Sunday, Prime Minister David Cameron suggested the vote could be held as early as this summer.