Both shows main character is a "shorty" who wants to become the best in their sport of choice. For Haikyuu that is volleyball and in Hinomaruzumou its sumo.
They are both really hard working, hard working at their sport. Probably works harder than anyone else just because they're both at a disadvantage because of their height. To counter their disadvantage, both main characters have to resort to certain techniques to win over their opponent.
There are also similar events in both series, one is when the Sumo team and Volleyball team comes back from a tournament, they are welcomed back by their school for their hard work, and geting attention was something neither of the shows clubs got before they went to a tournament.