Footage shows the panic and fear of the players and spectators in Pleasantville, New Jersey last night.
Some ran for cover, while others threw themselves to the ground.
A child and a man were seriously injured in the attack that took place around 8.30pm local time on Friday, according to officials.
The child’s condition was said to be serious and he was airlifted to a children’s hospital in Philadelphia.
No one had been arrested as of Friday night, and authorities were investigating whether more than one gunman might have been involved.
Authorities did not identify victims or release information on their conditions other than to say both were alive several hours after the shooting.
It comes after the suicide of a 16-year-old boy who killed two teenagers when he opened fire on students at a high school in California on Thursday morning.
In New Jersey, Kevin Minnick, a sports reporter who was covering the game, shared video from the scene of ambulances on the field.
“Pop, pop, pop. At least a half dozen shots in Pleasantville bleachers,” he wrote on Twitter.
“Got to say my knees are shaking,” he said, adding: “In 30-plus years, I’ve never witnessed anything like this first-hand. I hope to never witness it again.”
In footage shared by Mr Minnick, small children can be heard crying while parents carry their young ones home.
The shooting happened during a game between the Camden Panthers and the Pleasantville Greyhounds.
