In a video that is in wide circulation, Balakrishna, who is a legislator of the state's ruling Telugu Desam Party (TDP), is surrounded by fans and supporters. One of them appears to stumble and fall on him as he tries to take a selfie with his idol. The actor slaps him and pushes him away.
Balakrishna then walks away angrily.
The 57-year-old actor-lawmaker, popular as "Balayya" to his fans, is the son of former Chief Minister NT Rama Rao or NTR, a southern film legend.
Campaigning for the Nandyal by-poll on August 23 has been politically volatile with opposition leader Jaganmohan Reddy's outrageous comments last week on political rival Chandrababu Naidu.
Mr Reddy was issued notice by the Election Commission for saying that he would find it hard to object to Mr Naidu being "shot dead on the road". Later, he topped the comment with another one: "For your mistakes and betrayals, nothing wrong if you are punished with hanging."