If he was hit on purpose, you could sue the person who hit him--but probably not the resort; the resort is not responsible for criminal acts (and purposefully hitting someone in the face is a criminal act: assault) unless it was performed by a resort employee in the course of his or her job (e.g. if the employee was a beach or pool guard, thought you son was not allowed there, and hit him to keep him out). If he was hit due to negligence, such as not securing a table umbrella properly, so that the wind pulled it away and hit him, then you could sue the person who was negligent, or careless--and potentially the resort, if it was their employee who was negligent while doing the job (e.g. a waiter who impropely set up an umbrella at an outdoor cafe).If it was no one's fault--an umbrella was being held by someone when an unexpected wind gust pulled it away--then you cannot sue. There must be fault (negligence, or an intentional bad or wrongful act) to sue.