Enjoy oneself unrestrainedly; frolic.
1. Diversion from work or serious matters; recreation or amusement.
1.1 A pastime, game, or sport.
“Disport” is an interesting change-up from the usual “amusement” words – “play,” “entertain,” “recreate,” etc. I think the key grammatical point is to remember that in this form it’s a transitive verb (meaning it needs an object). Usually one disports oneself.
It can also mean “to frolic,” apparently. I suppose a protagonist might happen across jolly (and devious) little elves disporting in a forest glade, probably beside a fairy ring.
Though larger creatures can disport themselves, too:
There is a story about the captain of a freighter who, summoned by his first mate to see an indubitable sea serpent disporting itself a few yards to the port of his ship, refused, on the reasonable ground that if he saw the sea serpent he’d have to put it in the log, and he didn’t want to be known as a man who saw sea serpents all the rest of his life.
– Margaret St. Clair, “The Bird” (1951)