This is very nice simple style, nice neck detail with 2 colors, a little suggestion could be inside or outside(back side of t-shirt) of neck add little inscription making reference to Polska, and in the left arm side make the same logo of right arm or in the same left arm side add little polish flag. Overall great design :wink:

first thing first, i hate nike. anyway, great design man. its simple but beautifully put together. great job!