Police on Thursday said they have arrested an 87-year-old man over the attack at Yuen Long MTR Station on July 21, 2019.
A force spokesman said the man was being detained on suspicion of rioting and conspiracy to wound with intent.
Last month, the District Court jailed seven people to up to seven years in prison each, after they were convicted of rioting and other offences.
At least 45 people were injured in the violence in Yuen Long.