Shikotama: Love Baseball

Gouriki Tama, a girl with dreams of playing in the Japanese high-school baseball championship series (the Summer Koushien), enrolls in the elite baseball school, Kokusai Tenjou Senior High School, and tries to join the team as their starting pitcher. However the team captain, Tachibana Sukekiyo, rejects her because she is a female. There she decides to form her own team that will beat Sukekiyo's team and become the official baseball team of Kokusai Tenjou High. Her first recruit is a kindred spirit by the name of Oseki Shiko, a powerful sumo wrestler who was refused entry onto the school's sumo team also due to her sex. Shiko becomes Tama's catcher and the two form the "Shikotamas" whose goal is to take down the all-boy school baseball team and qualify for the Kouchien.

(Source: Wikipedia)