ride horseback vs horseback riding

ride horseback is not a noun while horseback riding is a noun.

Word	Noun	Adjective	Verb	Adverb
ride horseback	No	No	Yes	No
horseback riding	Yes	No	No	No

ride horseback (noun)	horseback riding (noun)
	travel by being carried on horseback
	the sport of sitting on the back of a horse while controlling its movements

ride horseback (verb)	horseback riding (verb)
ride on horseback