Clarification: over 40% of young men in the US have been arrested. (It is ambiguous whether "youths" refers to both sexes.)
(It is also possible to interpret the headline as saying that 40% of all youths worldwide have been in the US at some point, during which they were arrested, but I doubt many people were confused by that.)
(It is also possible to interpret the headline as saying that 40% of all youths worldwide have been in the US at some point, during which they were arrested, but I doubt many people were confused by that.)