UPDATE: 3.30pm BST
A spokesman for Smith said: "It was off script and on reflection it was an inappropriate choice of phrase and he apologises for using it."
Labour leadership challenger Owen Smith risked allegations of sexism after he declared that his party should "smash" Theresa May "back on her heels" during prime minister's questions. The Pontypridd MP made the comments during a major speech in Orgreave, South Yorkshire, on Wednesday morning (27 July).
But Smith, 46, defended his language when pressed by journalists. He stressed that the remarks were "rhetoric" and said Labour should be standing up for people. "I don't literally want to smash Theresa May back. I'm not advocating violence in any shape or form," he stressed.
The former shadow work and pensions secretary unveiled a range of policies, including a pledge to introduce a 50p tax rate, reverse cuts to inheritance tax and ban zero-hours contracts.
Workers' rights were at the heart of Smith's speech, with another commitment to bring back wage councils, which were scrapped under Margaret Thatcher.
The left-wing policies indicate Smith is attempting to win over some of Jeremy Corbyn's supporters, after the Islington North MP won almost 60% of the vote in Labour's 2015 leadership election.
"We welcome Owen's focus on equality of outcome, reindustrialisation and workers' rights – and his support for policies announced in recent months by Jeremy Corbyn and John McDonnell," a spokesperson for the Jeremy for Labour campaign said.
"We are delighted that he has echoed John McDonnell's call for the reinstatement of a Ministry of Labour, made last month at the Institute of Employment Rights (28/6/16), and Jeremy Corbyn's call for a ban on exclusive workforce recruitment from abroad, made during the referendum campaign, among other policies.
"Owen's speech today shows the leadership that Jeremy Corbyn has demonstrated in placing economic justice and fairness back at the heart of Labour politics. Under Jeremy, Labour has put restoring dignity and pride in our communities worst hit by decades of neglect at the core of our politics."