According to security at the stadium, an access panel to one of the endzone LED display boards dislodged and fell into a seating area around 12:45 p.m.
The panel landed on one fan. He was transported to the hospital. Officials do not believe the injuries are life-threatening.
Some witnesses say they saw the commotion but didn't know exactly what had happened.
It was about 45 minutes after kickoff when Texans fan Scott Byrne says he captured a photo of the panel that fell as it was being carried out by stadium staff.
Byrne said at first some fans thought a drink had been thrown.
Many fans left the game celebrating the Texans' victory, unaware of what had happened.
"I didn't hear about it until you told me just now," Celso Hernandez said. "I hope he's OK, and prayers go out to his family."
This isn't the first incident involving fans as the football season gets under way.
Jonathan Kelly, 25, fell about 60 feet to his death during the Texans pre-season game against the Vikings on August 30. Kelly was seen riding the handrails of an escalator several stories high. The medical examiner ruled his death an accident.
"It was a happy day but it was unfortunate someone got hurt," Will Beinert said. "That's always a sad thing."
There was also a video posted by a fan on YouTube that showed a brawl in the upper deck. The person who uploaded it says it's from the August 18 Texans-49ers preseason game. The verbal confrontation turned physical before it appears the people involved broke it up themselves.
"It's unfortunate," Becca Breinert said. "Everybody is here for the same reason, trying to have a good time. You meet amazing people."
As people left the stadium Sunday evening, their thoughts turned to their fellow fan who was just there to cheer his team on.
"I feel sorry for him. Golly, I saw the gash on someone's phone and it was bad," Izzy Vences said. "I don't know how badly he's hurting or how he feels but he deserves something out of it, I think."
Byrne says about six to eight seats were empty in the area where the object fell Sunday, but some of those fans were in their seats for the second half.
Reliant security also said there was a medical incident on level 5 Sunday, believed to be a heart attack. The man was stable when he was transported to the hospital.