As a native American-English speaker, I can tell you 'spoilt' does not sound natural. '
Spoilt' would be better applied to food that has gone bad.
'Damaged' would be the better option of the two.
You might also refer to how the card was damaged, such as "You bent the card" or "You crumpled the card."
ell.stackexchange.com/users/69483/Shino
Although it's somewhat hyperbolic, the expression 'you've ruined it' comes to me in this situation.
Whilst the card will hardly be in ruin, someone annoyed about its being damaged may still simply complain that it was 'ruined', i.e. rendered in an unacceptable condition.
‘Spoilt’ does sound perfectly natural to me as a British speaker; damaged is obviously correct but, because it's so literal, sounds strange, given nothing is being conveyed that the addressee can't already work out.
ell.stackexchange.com/users/96288/ben
Specifically for cards, you have "marked" it.
That's what makes it completely unplayable.
Marking a card means you can track it through the deck.
ell.stackexchange.com/users/40506/Aaron McMillin
In British English 'spoilt' and 'spoiled' are equally correct past participles of the verb 'spoil'.
In American English, only 'spoiled' is usually considered correct.
Other verbs like this include 'burn':
burnt/burned (British) burned (American), and learn: learnt/learned (British),
learned (American).
I would prefer to use spoilt/spoiled since the card is no longer suitable for use in a card game, even though it is not completely destroyed.
ell.stackexchange.com/users/46805/Michael Harvey
Native Brit; to me the meaning of spoilt / spoiled in this context would mean the card were no longer usable in the game, for example if someone wrote the denomination on the back of the card for all to see.
I would expect that particular usage to be uncommon in comparison with something like ruined .
To damage or bend a card doesn't necessarily render it unusable.
ell.stackexchange.com/users/96353/Inspector Squirrel
The reason why the current accepted answer states that it doesn't sound natural to say a "spoilt card", is because the comment not quite correct.
You have damaged the single card - but spoilt the whole deck and the game.
The difference between them is that when goods are damaged, it's very rare in English culture to look at the components individually; but the functionality of the product as a whole.
The product is not a single card, but the whole deck...
ell.stackexchange.com/users/56882/UKMonkey
Two people were playing cards. So a person folded a card by mistake. So what sounds natural:   You have spoilt the card.  You have damaged the card.   Do both "spoilt" and "damaged" sound natural?
You've spoiled/damaged the card
ell.stackexchange.com
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ell.stackexchange.com/questions/212813
ell.stackexchange.com/users/88627/It's about English
 'Damaged' would be the better option of the two. In British English 'spoilt' and 'spoiled' are equally correct past participles of the verb 'spoil' though  In American English, only 'spoiled' is usually considered correct. I would prefer to use spoilt/spoiled since the card is no longer suitable for use in a card game, even though it is not completely destroyed. "Damaged" sounds more natural than "spoiled" but there are many other options including "burn" and "marked" which are more suitable.
"Damaged" sounds more natural than "spoiled" but there are many other options including "burn" and "marked" which are more suitable.