A scrum began after the Falcons were awarded the ball.
Fox was on the field trying to restore order as players from both teams shoved each other.
As Samuel was walking away, Broncos guard Zane Beadles ran into him and knocked him down.
Samuel quickly jumped up, and Atlanta defensive end Ray Edwards appeared to throw a punch at a Denver player.
Manning had a 31.2 passer rating in the first quarter.
On Sunday, Manning’s brother, Eli, threw three interceptions in the first half then rallied the New York Giants to a 41-34 victory over the Tampa Bay Buccaneers.
After Moreno’s fumble, the Falcons ran 10 plays before Bryant kicked a 42-yard field goal for a 13-0 lead.
The Falcons were trying to snap a six-game losing streak on Mondays, including 0-3 under coach Mike Smith.
Their last Monday win came over New Orleans on Dec. 12, 2005.