Reports of an altercation involving a group at Portslade railway station resulted in the arrest of a man yesterday (Thursday).
Police descended on the area at 3.40pm yesterday afternoon, after one of the four men involved was said to be in possession of a knife.
Further enquiries led to the arrest of a 20-year-old man from Portslade on suspicion of affray - he remains in custody.
The group are thought to be known to each otherr and there is not thought to be any wider threat to the public.