Police are investigating a report of an altercation involving two men in High Street, Selsey at 2pm on Wednesday (28 April).
Sussex Police told V2 Radio that a 27-year-old man suffered a serious injury requiring hospital treatment.
A 48-year-old man was arrested on suspicion of causing grievous bodily harm with intent and has been released on bail, subject to conditions, while enquiries continue. The victim and suspect are known to each other.
District Commander, Chief Inspector Jon Carter said “I know this incident will have been alarming to anyone who saw it. We do not believe that there is an ongoing risk to the wider community as a result of this, and will conduct a rigorous investigation into this incident.
"Sussex Police is committed to catching criminals, protecting our communities and providing an excellent service. We had already stepped up proactive policing patrols in Selsey prior to this incident, but we do really need the support of the local community in telling us what is happening.
"I would like to thank those people who reported the matter to police, and for those who are working with investigators to assist us in understanding what happened. If anyone has, or is aware of any privately held footage of the incident, then please assist us by making this available to investigators."
Anyone with information or who witnessed what happened is urged to report online or call 101, quoting 755 of 28/04.