What makes a sport?

What are the definitions of a sport? The Sports Reflector has two requirements: physical demand and competition.
First, for an activity to be considered a sport, it must be physical. A participant must have to make use of his physical body in some way. Billiards rarely raises a sweat, but it demands a physical skill, so it is a sport. Chess requires no physical skill and is not a sport. Just because poker is on ESPN does not make it a sport.
Second, the activity must be competitive. Hiking requires cardiovascular activity and balance and oil painting requires hand-eye coordination, but neither of these pursuits are competitions, and they are not sports.