Bronny James Jr., himself a star at Sierra Canyon, was playing in an away game in Springfield, Mass., when the incident occurred. His father, who would play in an away game later that night against the Boston Celtics, was at his son's game and flanked by security guards.
A referee could be seen in video stopping play and security was called to remove the fan. However, no one was ejected because the fan couldn't be identified, reports say. Some described the object as resembling a piece of candy or trash.
James, 35, spoke with reporters after his Lakers lost to the Celtics on Monday-- telling them the incident "made me mad" and was "disrespectful," according to ESPN.
James said he didn't see the throw until after the game, the outlet reported.
"It's just disrespectful, and it was a little kid, too. I don't know how old that little kid was, so I don't know if he learned that on his own, or if he learned it at home," James said. "Whatever the case may be, it's disrespectful. I wonder how old that kid is if he is the age around Bronny's age or Bryce's age. I'd like to see them try that while they're paying attention."
James also responded to a slow-motion video of the incident that he was tagged in on Twitter.
Sierra Canyon lost its third game of the season 70-62. James, 15, came off the bench, playing 13 minutes and didn't speak to reporters after the contest, the outlet said.
His teammates and father spoke about how he's handled the extra attention being the son of an NBA superstar.
"He's cool, calm, he's better than his mom and dad. Let's just say that. He is, he's better than his mom and dad for some of the things he lets off his shoulder. I guess he's taken some from me too because I let a lot of s--- go too," James said, according to ESPN.
"He's a great kid. Most importantly, he loves being around his teammates, being a great kid, being a model citizen in the community, and playing the game he loves to play. And being a big brother to his brother and sister, but that s--- earlier made me mad when I saw that, it was just disrespectful."