Is it normal for someone to walk behind someone like this?

When walking how often does someone tail someone very closely and stay very closely behind the person as they walk at a brisk pace? When I was walking toward someone, I saw someone I kinda knew walking very closely behind someone. Here's a image to illustrate.

http://oi45.tinypic.com/m9vitv.jpg

black = me
red = person who is walking closely behind another
orange = some random person