A man armed with an iron bar assaulted two teenage boys in an attempted robbery near a Sheffield park.
South Yorkshire Police said he pulled up in a dark Audi A3, approached a group of teenagers and demanded that they handed over their mobile phones.
He used an iron bar to attack two of his victims, leaving one with a serious cut to his head.
The offender struck near to the entrance to Charnock Park, just off Carter Hall Lane, Charnock, at about 10.30pm on Wednesday, July 6.
A police spokeswoman said: "The man is believed to have got out of a dark coloured Audi A3, which pulled up just outside of the park gates.
"The man is then said to have approached the group, demanding they hand over their phones.
"It is then alleged that he assaulted two 17-year-old boys in the group with what is believed to be a small iron bar.
"One of the boys suffered a serious cut to his head. No one else was injured during the incident and the group then ran from the park."
The offender was white and is thought to have been wearing a black, hooded puffa jacket.
Witnesses or anyone with information should call South Yorkshire Police on 101.
Crimestoppers can be contacted anonymously on 0800 555111.