"I like games of football."
Translation:Dw i'n hoffi gemau pêl-droed.
Right. But I would translate that into English as "football games".
But Duolingo gave me the English sentence "I like games of football." Genitive, not adjectival. I believe I translated it as "Dw i'n licio gemau o bêl-droed," and got dinged for it, but at this point I can't remember for sure.