The 17-year-old boy is one of six people arrested on suspicion of grievous bodily harm after a man in his 30s was assaulted while walking along Fort Road at around 8.55pm on Sunday (June 2).
The victim was punched in the head and suffered a minor stab wound, according to Sussex Police. He was taken to the Royal Sussex County Hospital for treatment.
Officers conducted an extensive area search and six people were arrested.
Three 16-year-old boys, a 19 and 22-year-old man, all from Newhaven, and the 17-year-old boy from Hastings were all arrested on suspicion of grievous bodily harm. All six remain in custody and enquiries are ongoing.
Anyone with information to aid the investigation should report either online or call 101 quoting 1324 of 02/06. Police are particularly interested in speaking to the driver of a van who may have had a discussion with the group of suspects before the assault.