A man was assaulted after disturbing a group of intruders in Yapton, near Arundel.
The victim was passing a building site that backs onto Goodhew Close at about 7.15pm on Wednesday April 30 when he noticed men acting suspiciously on the site.
The 62-year-old shouted to the men but then continued to walk along the footpath eastwards towards Fordwater Gardens.
A man then ran towards the victim from behind and punched him in the face. He fell to the ground and saw three men running off.
He suffered a cut to his head and a black eye and had two teeth knocked out.
The attacker was 5' 10", white, tanned, about 30 and of athletic build. He had close cropped hair and a beard and was wearing a tracksuit top.
PC Michelle Denyer said: "We are trying to find anyone who saw the victim being punched or his attackers running off afterwards.
"This was an unprovoked attack that has caused the victim some nasty injuries and we need to speak to anyone who could help find the men involved."
Anyone with information should call 101 quoting serial 1343 of 30/4, email firstname.lastname@example.org or call the independent charity Crimestoppers anonymously on 0800 555111.