What does it mean when a guy puts his head down while walking past you?

Well a month ago i caught him staring at me from afar. It was pretty crowarded and kinda dark. We made eye contact. Its like he followed me with his eyes, because the second time i caught him he was already staring at me. This all happened a month ago. Last week I saw him as soon as he saw me through the door, he put his head down and hand in his pocket while walking past me, he was walking quickly and was walking to class. It was like he was avoiding me and kinda nervous.
What does it mean when a guy puts his head down while walking past you?
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