This same thing happens in the central square of Marrakesh to female western tourists including Muslim women as well if not veiled.  Gangs of teen boys roam the square when it is crowded and even more so at night targeting young Western women for a gang gropings..  

Even a Canadian Muslim friend was groped after which she vowed never to set foot in that country again.  Eventually the younger women in the group could only travel in Marrakesh if they had a male escort at all times.   

These behaviours are tolerated by local police and so it is not a surprise that the same behaviour shows up in European countries when there are large crowds with young women.

The politically correct would rather just turn a blind eye to this unacceptable behaviour and continue to import more and more unvetted young men from north Africa.  The political elite have brought their societies to this end point by their own doing in Europe.