Ride High with the Wave by Sharon K. Solomon
Hiro Kojima and Ted Richman are backstroke rivals on the Dolphins, their swim team. Hiro is the new boy in town and Ted dislikes him. Reluctantly, Ted agrees to work with Hiro to solve their mutual problem, attending swim meets on Saturdays when Ted and his family attend Sabbath services and Hiro goes to Japanese school. The rivals join forces to change swim meets to Sundays. Will they succeed? And how will they resolve their rivalry?
(via Jewish Book Council)