Sunday Night Football came to a halt late in the third quarter last night ... when a fan with a Pro-Donald Trump sign ran on the field -- all while the former U.S. President was in the building!
The woman's sign read ... "TRUMP SECURE BORDER" and "KAMALA OPEN BORDER"
Ultimately, security corralled the fan (who people are saying is IG model Claudia Rose) near the 50-yard line ... and she went without a fight.
As the woman was led away, chants of "USA! USA!" broke out in chorus around Acrisure Stadium in Pittsburgh.
While it's unclear what President Trump thought about the incident, he seemed to be lovin' his time in The Steel City, pumping his fists during the chants.
On the field ... Trump saw Russell Wilson pick up his first win as Steelers starting QB, beating Aaron Rodgers and the Jets, 37-15.
It marked the end of a massive push in the critical swing state of Pennsylvania for Trump ... who even held a campaign rally with former Steelers stars Antonio Brown and Le'Veon Bell on Saturday.
AB made his thoughts on Kamala Harris' running mate, Tim Walz, crystal clear.
We reached out to Pittsburgh PD for information about the incident ... but have not yet heard back.