If you're looking for manga similar to One Piece: Take Aim! The Pirate Baseball King, you might like these titles.
Yuugou, who grew up in the USA and has been madly in love with baseball since he was very young, returns to Japan and enrols in an academy known for its impressive reputation in high school baseball... Only to discover its "legendary" team in shambles.
Enter our hero Wakadaishou! He doesn't have much interest in school; he saves his energy for all the excitement he can stir up after school. This is an early Adachi Mitsuru 'youth manga', filled with engaging characters, comic scenes, and a young hero with a zest for life.
Persistent mediocrity hasn't dissuaded Fukutsu Toshi, captain of a lame high school baseball team, from his love of the game. But when the principal, dissatisfied with their winless performances, threatens to take away their playing field, Toshi is forced into action to turn things around with all out effort. But facing him at every turn is endless adversity. Nothing is ever easy for him, but luckily, Toshi has the determination to beat it all.