The incident occurred in Montague Street in Worthing at 4.25pm on Thursday (April 27), police said.
PC Gregory Brown said: “Members of the public reported seeing the man, described as white, in his 20s, of slim build, with facial hair and black hair, being punched on the back of the head.
“However this man has yet to come forward.
“Please get in touch if you are this man, or if you saw this incident.”
A 28-year-old man from Worthing was arrested on suspicion of common assault and using threatening or abusive language, a police spokesperson said.
He was questioned and released under investigation, confirmed the spokesperson.
You can email the police at [email protected] quoting serial 981 of 27/04
You can also report online to https://sussex.police.uk/contact-us/response-to-appeal/ or call 101, or contact the independent charity Crimestoppers anonymously on 0800 555 111.
Don’t miss out on all the latest breaking news where you live.
Here are four ways you can be sure you’ll be amongst the first to know what’s going on.
1) Make our website your homepage
2) Like our Facebook page
3) Follow us on Twitter
4) Register with us by clicking on ‘sign in’ (top right corner). You can then receive our daily newsletter AND add your point of view to stories that you read here.
And do share with your family and friends - so they don’t miss out!
Always the first with your local news.
Be part of it.