Before the tussle, press outside the building had been told they would not be let in. But then a US official said they were allowed.
Video shows a woman shouting for the US pool to enter amid a din of voices.
"The North Korean security was a little overzealous, at times trying to block US reporters' view," wrote Jennifer Jacobs, a senior White House reporter at Bloomberg, adding that the clash "came to body blows."
North Korean security tried to block U.S. media access during President Trump's meeting with North Korean leader Kim Jong Un on June 30.
Later, Grisham could be seen directing reporters outside the House of Freedom and was with Trump at the DMZ, according to CNN.
Grisham and the White House did not immediately respond to a request for comment.
On Sunday, Trump briefly stepped across the border while meeting Kim in the demilitarised zone between North and South Korea four months after the leaders' last nuclear talks broke down in Vietnam.
Sunday's private discussions, which lasted almost an hour, were billed as reopening the fraught negotiations.
"Speed is not the object, we want to see if we can do a really comprehensive, good deal," Trump said afterward. "Nobody knows how things turn out, but certainly this was a great day, this was a very legendary, very historic day."
Grisham has spent two years as communications director for first lady Melania Trump and replaced Sarah Sanders as White House press secretary last week.
Like Sanders before her, Grisham has been critical of the media and has "developed a reputation as a pugnacious defender" of the First Lady, as The Washington Post reported Tuesday when Grisham's new role was announced.
Grisham, 42, has sometimes adopted a sharp tone in her statements - something traditionally not seen from the East Wing but in tune with the often confrontational stance of the Trump White House's press operations.
When the president went after MSNBC host Mika Brzezinski in the summer of 2017, claiming falsely in a tweet that she was "bleeding badly from a facelift," Grisham defended Trump: "When (he) gets attacked, he will punch back 10 times harder."
Grisham is keeping her role as the first lady's spokeswoman as she takes on the press secretary job.