A 17-year-old boy was attacked by someone with a claw-hammer and is in a critical condition.
The attack happened in an underpass in Bilston Street, Wolverhampton, on Thursday evening following "an argument".
Police said the teenager had serious head injuries and underwent emergency surgery last night.
Det Sgt Chris Jones said it was a targeted attack and needs people to come forward with information.
He said: "At present we understand this was a targeted attack, but believe there are more people that have information about what happened and why."