Sport is a character-name with a very specific pop-cultural home: Sportacus from LazyTown, the Icelandic children's show (2004–2014) starring Magnús Scheving as an athletic, positivity-radiating superhero. As a male pet name at rank 2677, Sport almost certainly draws from this reference for younger owners — or from the more general term for an athletic, game dog in the old-fashioned American usage.
The LazyTown Connection
LazyTown became a genuine cult phenomenon, with Sportacus — the mustachioed, eternally energetic hero who encouraged children to exercise and eat "sports candy" (fruits and vegetables) — becoming a meme and an affectionate cultural touchstone. Naming a dog Sport or Sportacus after this character is a tribute from an owner who grew up with the show and found the positivity genuinely contagious. The full name Sportacus also appears in pet naming data for the same reason.
The Old-American Usage
Before LazyTown, Sport was a term used for a game, athletic dog in the American sporting tradition : bird dogs, retrievers, and field dogs were often called Sport in the era when hunting dogs were essential working animals. Labrador Retrievers and English Springer Spaniels carry the sporting tradition authentically.
The Counter-Reading: Two Very Different Registers
Sport from LazyTown and Sport as a sporting-dog name are tonally miles apart — one is cheerful children's television, one is old-fashioned rural pragmatism. Owners should know which one they're invoking, since the two audiences will read the name very differently at the dog park.