Crossword Genius

Hounds romping in North American river (6)

Ross

I believe the answer is:

hudson

I'm a little stuck... Click here to teach me about this clue!

Here is my best explanation:

'river' is the definition.
(Hudson is an example)

'hounds romping in north american' is the wordplay.
'hounds' anagrams to 'HUDSON'.
Though, I am unsure how this is indicated.

Can you help me to learn more?