Why did this large billed crow attack me?

A few minutes ago, I was walking outside when a large billed crow flew over my head pretty close. I figured that since I'm in a big city, maybe it's just more used to people than the crows in my rural area. But then it flew over me again and brushed my head which was a little weird. I also noticed that it was following me and cawing at me. Then, it actually landed on my head and pulled my hair. I went into the subway station to hide from it. Why would it follow me and attack me like that? I didn't do anything to it and it was only going after me.