When it's a counterfeit.
Over the years, there's been a lot of talk about clones in the games industry, but after reading this article on Indie Statik about an Android game called Slap!, I think we (the industry) need to be clearer in our word choice.
It's easy to throw the word "clone" around, but this incident - where the copycat game is "actually using the original sprites from our game" - I'd like to suggest a different term:
counterfeit: adj. made in exact imitation of something valuable with the intention to deceive and defraud. (OED)
I think that's a much clearer description of what's happened in this case, and should be targeted by a DMCA.
(As an aside, I do find it amusing that Slap! is "based on" the traditional game "Red Hands", but the creator appears to claim that a Windows game called Hand Smash has "ripped off the [Slap!] mechanic".)