was greeting a crowd in the city of Morelia on Tuesday when someone apparently grabbed him by the hand and wouldn't let go.
The worshiper ended up pulling the Pope down onto a young man in a wheelchair.
Francis regained his balance with the help of a security guard. But his normally smiling face morphed into a look of anger as he apparently yelled at the person in the crowd.
Shortly afterward, an announcement came on the stadium's speakers:
"We are asking you to be careful," the announcer said. "Please contain yourself. Pope Francis wants to greet us, but if we pile up, it will be difficult to do so."
He's known for interacting closely with worshipers -- for example, opting for a car with an open top instead of the traditional bulletproof "Popemobile."
But the incident in Morelia might have his security detail on higher alert.
On Wednesday, the Pope will visit the notoriously violent city of Juarez, Mexico. Juarez, once known as the "murder capital of the world," sits just across the Rio Grande from El Paso, Texas.
Francis has spoken out against impenetrable international borders, calling them "monuments of exclusion" and even a "form of suicide" that closes countries in on themselves. He has also urged the United States and Mexico to protect Central American migrants
, particularly children, seeking to escape poverty and violence.
"I don't think the Holy Father's trip to Juarez is political," said the Rev. Timothy Kesicki, president of the U.S.-based Jesuit Conference. "But how could it not have political overtones? It's going to be drawing a lot of attention to immigration at a time when we are having debates about it."
The moment many Catholics are most eagerly awaiting will come when the Pope approaches the U.S.-Mexico border in Juarez.
Papal aides say security and logistical barriers will prevent the Pope from making a political point by crossing the border.
Across the river and through the fences, a group of "Francis VIPs," including undocumented immigrants seeking asylum in the United States, await the Pope's blessing.
"These are the people the Pope has come to see and pray for," said Bishop Mark Seitz, the El Paso bishop who organized the event.
Francis is expected to say a prayer at the border fence and lay flowers in memory of the more than 6,000 migrants found dead on the U.S. side of the border between 1998 and 2013, according to U.S. Border Control estimates.
"The symbolism of this moment will not be missed by anyone in the border region," said Joe Boland, vice president of missions at Catholic Extension, a charity with a long history in the area. "It will be like the Pope coming to Ellis Island."
Later Wednesday the Pope will celebrate a large Mass not far from the border, where migrants and victims of drug violence will be among the 200,000 receiving Holy Communion.