Sakuragi Hanamichi is a delinquent who's so unpopular with girls that he's been rejected fifty times. Haruko Akagi is the only girl who isn't scared of him; instead she's impressed with Sakuragi's athleticism and, convinced that he would do well, introduces him to the Shohoko basketball team. Desperate to impress Haruko and believing that she is the girl of his dreams, Sakuragi joins the team in spite of his initial reluctance. Surprisingly, Sakuragi is a natural at the sport regardless of his reputation for being hot-tempered and immature. From now on Sakuragi must work together with his teammates, including his rival Rukawa, to fulfill their captain's dream of winning the national championship. That is, if they have what it takes!
To put it simply - Mr. Fullswing is refreshed, baseball version of Slam Dunk. Both are comedy sports mangas, with arrogant main character. The protagonist decides to join a sport club, since he have fallen in love with manager. Even though he knows nothing about the sport, his raw power makes him potentially a great player.
While Mr.Fullswing sometimes have too many gags (to a point, that it gets tiresome ) both mangas are amusing sport stories. If you like one, you should give the other one a try too.