Complex sentence: He then moved to New York City where he trained in a Sports Medicine fellowship at Lenox Hill Hospital, honing his skills both in the operating room and on the field by traveling with professional league teams and taking care of athletes throughout the season.
Split into simpler sentences: He then moved to New York City where he trained in a Sports Medicine fellowship at Lenox Hill Hospital. As a part of the fellowship, he traveled with professional league teams and took care of athletes throughout the season.