I wanna dress like Blair for gym, does anyone know how i can get the look she did in the episode she played lacrosse?

Well it all depends on what your school will allow. Do you have to wear a uniform? Does your outfit have to be a particular colour? Can you wear a skirt?

If you have a uniform it will probably consist of a polo top. If you dont, you can always buy one fairly cheaply and in heaps of different colours. Polo tops are great for sport becasue they are so comfortable. Blair wears hers buttoned up.
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Blair tucks her polo topo, início into a sports skirt, which you can also get in a range of clours and styles from sports shops. Blairs saia is very short, so you would have to also get maybe short bike shorts to go underneath.
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Blair teams all this with High socks: link
a wide belt: link
sweat bands:link
And a neat, pulled back hairstyle:link

I dont think you see her shoes, but I think this is the one time when she does not wear heels :]