They're shy around you.
If girls are shy around you, act weird or just goes quiet around you it means they like you they may only talk to you if needed like group work.
Personal experience:
Personally when ever my crush talks to me I say a few letter words or when he goes to high 5 me I get nervous freeze up and just doesn't say anything but if it was group work I could easily talk to him except I can't ever look him in the eye.
