A video posted on X by the Communist Party of India (Marxist) showed one of its lawmakers, John Brittas, being helped from a bus to an autorickshaw as he appeared to be in distress.
Reuters could not verify claims about detainees being assaulted by police.
The Delhi Police spokesperson did not respond to calls made by Reuters to seek comment.
The youth movement is one of the biggest political challenges to Prime Minister Narendra Modi in his 12 years in power, during which his Bharatiya Janata Party (BJP) has repeatedly swept the polls and eliminated any serious challenge by opponents, including the Congress Party.
The protesters are calling for the resignation of Chief Election Commissioner Gyanesh Kumar over a revision of voter lists that critics say disproportionately benefits Modi.
