What hobby is it?
Table tennis
What hobby is it?
Surf / surfing
What hobby is it?
Cycle / Cycling
Are they surfing?
Yes, they are.
What hobby is it?
Skateboard / Skateboarding
Are they doing Judo?
No they aren't. There playing chess.
Are they playing chess?
No, they aren't. There sailing,
Are they sailing?
No, they aren't. There surfing.
What hobby is it?
Basketball / Playing basketball