Það var stigavörðurinn sem stokkaði spilastokkinn.

This is a cleft sentence, used to put special focus on one part of the message. It is very close to English It was X who Y.

So Það var stigavörðurinn sem stokkaði spilastokkinn means, structurally, It was the point guard who shuffled the deck. The emphasized part is stigavörðurinn.

A more neutral version would be Stigavörðurinn stokkaði spilastokkinn.

Here það is like the it in English It was John who did it. It does not point to a specific object or idea. It is just part of the cleft construction.

So in this sentence, það is a grammatical placeholder, not a literal it.

Sem introduces the relative clause sem stokkaði spilastokkinn, which means who shuffled the deck.

In Icelandic, sem often corresponds to English who, that, or which in relative clauses. It does not change form for gender, number, or case.

It is the definite article: Icelandic usually expresses the by attaching it to the end of the noun.

So:

• stigavörður = a point guard / a scorekeeper
• stigavörðurinn = the point guard / the scorekeeper

That final -inn is the noun plus the.

Because it is the focused noun phrase in an identifying sentence with vera (to be), and in Icelandic that kind of noun phrase is normally nominative.

It is also the understood doer of the action in the relative clause: the point guard is the one who shuffled. So nominative fits both the grammar and the meaning.

Because spilastokkinn is the direct object of stokkaði (shuffled), so it must be in the accusative case.

A useful comparison is:

• spilastokkur = a deck of cards, nominative
• spilastokkurinn = the deck of cards, nominative
• spilastokkinn = the deck of cards, accusative

English does not show this kind of noun-case change, but Icelandic does.

That is a normal declension pattern for many masculine nouns in Icelandic.

The nominative singular is spilastokkur, but in oblique cases such as the accusative, the -ur drops from the stem:

• nominative: spilastokkur
• accusative: spilastokk

Then the definite ending is added, giving spilastokkinn.

Both are past tense.

• var = past singular of vera (to be)
• stokkaði = past of stokka (to shuffle)

So the whole sentence is talking about a past event.

It is less neutral than a plain statement, but it is completely normal Icelandic.

Compare:

• Stigavörðurinn stokkaði spilastokkinn. = neutral statement
• Það var stigavörðurinn sem stokkaði spilastokkinn. = emphatic, focusing on who did it

The second version is especially natural if you are answering Who shuffled the deck? or correcting someone.

Yes. Icelandic uses compounds very often.

A helpful rule is that the last part of the compound is the grammatical head. That means the last part is what carries the case ending and the definite article.

So in these words, the endings show up on:

• -vörðurinn
• -stokkinn

That is very typical of Icelandic compound nouns.

A good beginner rule is:

• þ sounds roughly like th in thing
• ð sounds roughly like th in this

So in það, the first sound is like th in thing, and the last consonant is a voiced th-type sound. In actual Icelandic speech, ð can be lighter than an English th, but this approximation is a good start.

The same ð sound appears in stokkaði.