Alfie Kent, 27, was charged with throwing a missile at a spectators area during the EFL Cup tie at Selhurst Park on September 16.
He appeared at Croydon Magistrates’ Court on Wednesday, October 22, where he pleaded guilty to the charge.
Kent, of Green Street Green, was handed a £100 fine and a three year football banning order.
Ryan Leonard scored an injury-time equaliser for Millwall to cancel out Chris Richards’ opener for Palace, before the home team won 4-2 on penalties.
