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 te have to wear a uniform? Does your outfit have to be a particular colour? Can te wear a skirt?

If te have a uniform it will probably consist of a polo top. If te dont, te 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 superiore, in alto into a sports skirt, which te can also get in a range of clours and styles from sports shops. Blairs gonna is very short, so te 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 te see her shoes, but I think this is the one time when she does not wear heels :]