Where the shape comes from
Two figures facing off, hands raised or locked together in a grapple — as direct a picture of a fight as the script has. In the twentieth century’s simplification it was folded into 斗, the unrelated dipper radical, purely for its simpler shape, so that modern 斗争, to struggle, and 搏斗, to wrestle, to grapple, now share their written form with a measuring cup that has nothing to do with combat.
汉字 filed under 鬥
No published character on HSK Guide is filed under this radical yet. 汉字库.