Leikurinn var jafntefli.

Because -inn is the suffixed definite article in Icelandic.
So:

• leikur = game / match
• leikurinn = the game / the match

Unlike English, Icelandic usually puts the on the end of the noun instead of using a separate word.

Leikurinn is the definite form, meaning the game.
If you said Leikur var jafntefli, that would sound like A game was a draw, which is much less natural in this context.

So the sentence is talking about one specific game that both speaker and listener know about: the game.

Var is the past tense of vera (to be).

• er = is
• var = was

So:

• Leikurinn er jafntefli = The game is a draw
• Leikurinn var jafntefli = The game was a draw

Since the sentence refers to a completed game or a past situation, var is the correct form.

Because Icelandic has no indefinite article.
English says a draw, but Icelandic just uses the bare noun:

• jafntefli = a draw / draw

So the sentence is literally closer to The game was draw, even though the natural English translation is The game was a draw.

Jafntefli is a noun, not an adjective.

It means draw, tie, or drawn result in a game or match.

So this sentence is structurally like:

• The game was a draw
• not The game was tied as an adjective

If you want to think of the grammar, jafntefli is a predicate noun after vera (to be).

Because Icelandic nouns keep their own grammatical gender.

• leikur is masculine
• jafntefli is neuter

That is completely normal. The second noun does not have to change gender to match the first one.

In other words, Icelandic is not saying that the game somehow becomes neuter. It is simply using a neuter noun, jafntefli, to describe what the game was.

Leikurinn is in the nominative, because it is the subject of the sentence.

Jafntefli is also understood as nominative, because predicate nouns after vera are normally in the nominative in Icelandic.

So the structure is basically:

• Leikurinn = subject, nominative
• var = verb
• jafntefli = predicate complement, nominative

With jafntefli, you do not see a visible case change here, because the form stays the same.

Because the sentence is identifying the result as a draw, not the draw.

After vera, Icelandic often uses an indefinite predicate noun when saying what something is or was:

• Hann er kennari = He is a teacher
• Leikurinn var jafntefli = The game was a draw

If you said jafnteflið, that would usually sound much more specific and context-dependent, as if you were referring to one particular draw already known from the conversation.

No. This is the normal, straightforward order:

• Leikurinn = subject
• var = verb
• jafntefli = complement

So it follows the basic pattern:

Subject + verb + complement

That makes it a very typical beginner-friendly Icelandic sentence.

Yes, it is understandable and natural: Leikurinn var jafntefli means The game was a draw.

But Icelandic also often uses other expressions, especially in sports contexts, such as:

• Leiknum lauk með jafntefli = The game ended in a draw
• Leikurinn endaði með jafntefli = The game ended in a draw

So your sentence is good, but you may also hear these alternatives quite often.