A Utah Jazz fan caught Harden's attention as players came out of the locker room for the start of the third quarter during Game 2 Wednesday night.
In video recorded by Jason Glad, he can be heard saying, "You're still the worst flopper in the NBA."
Glad, who lives in Phoenix and is a diehard Jazz fan, told ABC13 that everything happened quickly.
"He (Harden) looked at me and slapped the phone. It all happened so fast," Glad said.
Glad said he's seen reaction from both sides -- some support and others questioning why he would get in the face of a player.
His video post on Facebook has been watched over 60,000 times.
Glad told ABC13 that he traveled to Houston for Game 1 and 2 to cheer on the Jazz.
But would he come back to Houston for Game 5?
Glad says he would love to, even for a possible Game 7.
Houston police says they are aware of the video.
"The department is aware of the video, however the individual who posted it has not filed a police report alleging a criminal offense," HPD said in a tweet. "The individual may contact us and file a report if he believes he was the victim of a criminal offense."
HPD also added that the department is conducting an administrative review.