A sport is part of a plant (an offset) that deviates from the rest of the plant. Actually "sport" is a convenient term used by gardeners, but it is not a genetic term. It is the end result of an earlier genetic process. In a sport the change has taken place in a leafbud (mitose), not in the flower (meiose). Three processes can be responsible for a sport to arise. In most cases it will be due to somatic recombination or chimaeral rearrangements and rarely due to a (back) mutation. Most sports can therefore only be propagated vegetatively. So a sport can be a chimaera, but also a recombination or rarely a mutant. A seedling is by definition never a sport.