If there's competition, it's a sport. If there's not competition, it's not a sport.
Hard work is not the defining characteristic of a sport. Construction work, army combat, and firefighting, for example, are not sports, even though they are extremely physically demanding. You say it's a sport because you work hard, with long hours. By that reasoning, musical and theatrical performance would be sports, because they work hard in long practices. But that doesn't work too well, because they are not sports. So, let's work with the following statement:
A sport is a competition in which success depends on the competitor's physical athletic skills.
Many activities have a sport form and a non-sport form. Cheerleading and dancing are examples of this. Cheerleading on the sidelines, not in competition, is not a sport. Competitive cheerleading is. Performance dance, even if it's with the New York City Ballet, is not a sport because there's no competition. Competitive dance is a sport.
But hey, just because something isn't a "sport," that doesn't mean it's not physically demanding. There are many jobs and activities that are not sports, but still more physically demanding than many sports. It's all about whether there is the athletic competition aspect to the activity.