A supporter had sadly suffered a medical emergency in the crowd.
And the official suspended play as medics rushed to help the stricken fan.
After several minutes, players from both sides then left the field as the emergency in the stands continued.
Rotherham tweeted: "A temporary pause in play for what appears to be a medical emergency in the crowd."
Another message added: "Players from both sides have been taken into the dressing rooms as the medical teams respond to the emergency.
"Our best wishes to the person involved."
Birmingham also tweeted: "We'll have a small break in play here owing to a supporter medical emergency. Sending our best wishes to those involved."
Nearly 20 minutes after players left the field, Rotherham tweeted again to reveal the fan had been whisked to hospital.
Both the supporter and medics at the scene received a standing ovation from the crowd.
Rotherham said: "The supporter has now left the stadium with medical professionals.
"We would like to thank everyone for their compassion and patience and it goes without saying that all our love and thoughts are with the casualty.
"We would ask that the supporter's privacy is respected at this incredibly difficult time."
Another tweet confirmed the game would shortly recommence from the 11th minute, making for a 37 minute delay.
It added: "The game will restart with the clock at 11 minutes at 3.45pm following a short warm up period for the two teams."
Another tweet thanked medics, reading: "We cannot put into words our gratitude to the paramedics, medical professionals and both sets of supporters for the incredibly compassionate way in which such a difficult situation has been handled.
"Sincerely, from every single one of us at Rotherham United, thank you."
At half-time, Rotherham then released an official club statement on the incident.
It read: "Everyone at Rotherham United would like to place on-record our sincere thanks to the paramedics, medical professionals and both sets of supporters for the professionalism and compassion which was displayed throughout the medical emergency at AESSEAL New York Stadium this afternoon.
"Our thoughts and prayers are with the supporter, who was taken to hospital from the stadium after being treated on-site by medical support from St. John's Ambulance and the respective doctors of both clubs.
"In unimaginably difficult circumstances it was incredible to see allegiances on the pitch put aside and the efforts of the medical professionals and support staff receive the commendation that they deserved from everyone inside AESSEAL New York Stadium.
"We now ask that the supporter's privacy is respected during this time."
The match was Steve Evans' first back in the Rotherham dugout after quitting Stevenage last week.
He previously managed them between April 2012 and September 2015.
And Evans' first task will be to lead Rotherham back to the Championship following Leam Richardson's sacking.
Rotherham have won just four games all season, leaving them 22 points off safety.
As for Birmingham, they are only out of the drop zone thanks to their superior goal difference over Huddersfield.
But with a game in hand, they will be eager to avoid relegation to League One after a dismal season which has seen them go through SIX managers.
John Eustace started the season in charge before being brutally sacked for Wayne Rooney.
Wazza then lasted just 15 games before Steve Spooner took charge of one match as interim boss.
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