In the city of Ravenna you can go jogging , there are good paths for that, roller skating if you wish, get a free bike at the tourist office for a day by leaving your document. There's one big stadium and a pool. I know there are some gyms, but I have never been at the ones in Ravenna, just I'm aware of their existance.
Best conditions for the sports are at the beach, the closest beach is Marina di Ravenna. in almost any beach establishment you'll find campgrounds for football, valleyball, racchetoni, sometimes basketball, table tennis.
Water bikes, cannoyas, scooters are for rent too, here you'll leave some money. At the port you can rent a boat. there's a diving school as well as some boat-parachuting in the sea from time to time.
tournirs of sport are organised constantly in summer, sometimes even on international levels (beach tennis or volley). Local competitions of racchettoni and a kind of da fames football.
Equipment: If you ecquipment at the beach establishment (balls, rackets) you can get them at the bar, for free, leaving id card or some valid document. Water bikes and etc. are for rent.