Hann hrópar stundum of hátt á leiknum.

Rough breakdown:

• Hann – personal pronoun he, nominative singular; the subject.
• hrópar – verb shouts/cries out, 3rd person singular present of hrópa.
• stundum – adverb sometimes (frequency).
• of – adverb meaning too / excessively (not the English preposition of).
• hátt – from the adjective hár (high, loud); here used adverbially = loudly.
• á – preposition at / on (here: at in the sense at the game).
• leiknum – the game / the match, dative singular definite of leikur (game, match).

So the structure is: He shouts sometimes too loud(ly) at the game. → idiomatic English: He sometimes shouts too loudly at the game.

• The infinitive is hrópa – to shout, to call out.
• hrópar is:
  • present tense,
  • 3rd person singular,
  • indicative mood.

Very roughly, hann hrópar corresponds to English he shouts / he is shouting, because Icelandic present simple often covers both uses where English distinguishes simple and progressive.

• Hann is nominative case (subject form) = he.
• Honum is dative case (an object or an indirect object form) = roughly to him.

In Icelandic, the subject of a normal active verb like hrópa is in nominative, so you must say:

• Hann hrópar … – He shouts …

Using Honum hrópar … would be ungrammatical here (unless you were in a special impersonal construction, which this is not).

The neutral word order here is:

• Hann hrópar stundum of hátt á leiknum.

Icelandic main clauses are generally verb-second (V2): some element first (here Hann), then the finite verb (hrópar), then the rest (adverbs, objects, etc.).

With adverbs like stundum, the most common positions in a simple sentence are:

• Hann hrópar stundum of hátt á leiknum.
• Stundum hrópar hann of hátt á leiknum.

Both are fine. The second version puts more emphasis on sometimes.

What you normally can’t do is break the V2 rule by putting stundum right after the subject and before the verb, e.g.:

• *Hann stundum hrópar … – this is wrong in standard Icelandic.

Here of is an adverb meaning:

• too, overly, excessively (before an adjective/adverb).

So:

• of hátt = too loud(ly).
• of kalt = too cold.
• of mikið = too much / too many.

It is not the same word as English of (the preposition). It’s a false friend; always translate this Icelandic of as too / overly, never as English of.

The base adjective is hár:

• hár – high, tall, loud (about sounds).

Icelandic often forms an adverb from an adjective by using the neuter singular form. For hár, the neuter singular is hátt, and that can function adverbially:

• hátt – loudly / high (as an adverb).

So:

• Hann talar hátt. – He speaks loudly.
• Hann hrópar of hátt. – He shouts too loudly.

You do not use the masculine form hár or a dative háum here, because you’re not describing a noun; you’re modifying the verb (shouting) → you need an adverbial form, which is hátt.

Both modify hátt (loudly), but they express different ideas:

• mjög hátt = very loud(ly)
  → strong, but not necessarily a problem.
• of hátt = too loud(ly)
  → implies it is excessive / more than is acceptable or desirable.

So:

• Hann hrópar mjög hátt á leiknum. – He shouts very loudly at the game. (maybe neutral, just descriptive)
• Hann hrópar of hátt á leiknum. – He shouts too loudly at the game. (clearly negative / critical)

á leiknum literally is:

• á – on, at (here: at as in at an event),
• leiknum – the game / the match (dative singular definite).

In this context, á is the usual preposition for being at or taking part in an event:

• á leiknum – at the game / match.
• á tónleikum – at a concert.
• á fundinum – at the meeting.

You would not normally use í (in) here, because that suggests inside something, rather than at an event. So á leiknum is the natural way to say at the game.

The noun leikur (a game, a match) declines like this (singular):

• Nominative: leikur
• Accusative: leik
• Dative: leik
• Genitive: leiks

With the definite article (“the”) attached, dative singular becomes:

• leik
  • -num → leiknum = the game (dative).

Now:

• The preposition á takes:
  • dative for location (where something happens):
    → á leiknum = at the game.
  • accusative for direction / movement toward:
    → á leikinn = onto / to the game.

Since the sentence is about shouting at the game (location), you must use dative → leiknum, not leikinn.

You also can’t use plain leikur because you want the game, not just a game, and the preposition á requires the correct case inflection after it.

You might hear í leiknum in some contexts, but there is a nuance:

• á leiknum – the normal expression for at the match / at the game (as an event).
• í leiknum – more like in the game, often with a sense of in the course of the game / in the gameplay itself.

In your sentence, where the idea is a person shouting as a spectator or participant at the game, á leiknum is the natural preposition. Í leiknum would sound more like during the game and might fit better in contexts talking about what happens in the play itself, e.g.:

• Hann skoraði tvö mörk í leiknum. – He scored two goals in the game.

Yes, that is correct, and quite natural:

• Hann hrópar stundum of hátt á leiknum.
• Stundum hrópar hann of hátt á leiknum.

Both obey the V2 rule (the finite verb hrópar is in second position). The difference is emphasis:

• First version: neutral emphasis on he (Hann).
• Second version: emphasizes sometimes (Stundum).

Orders that break V2, like:

• *Hann stundum hrópar of hátt á leiknum.

are ungrammatical in standard Icelandic and should be avoided.