Hann reyndi að spyrna varlega, en dómarinn flautaði of snemma.

Reyndi að means tried to. The verb is reyna = to try, and after it Icelandic normally uses að plus an infinitive:

• reyna að lesa = try to read
• reyna að sofa = try to sleep

So Hann reyndi að spyrna means He tried to kick.

Here að is the infinitive marker, like English to in to kick.

• spyrna = kick
• að spyrna = to kick

After many verbs, Icelandic uses this pattern:

• hann vill fara = he wants to go
• hann reyndi að fara = he tried to go

So in this sentence, að is not the preposition to in a directional sense; it is just part of the infinitive construction.

In this sentence, spyrna means to kick. In sports contexts, that is a very natural meaning.

Be aware that spyrna can also appear in other expressions, especially with particles or prepositions, where the meaning can shift a bit, for example toward push with the feet or resist. But here, with no object stated, it simply means something like kick.

Because the object is not necessary if it is obvious from the context.

This works a lot like English:

• He tried to kick carefully
• You do not have to say what he kicked if the situation already makes it clear.

So að spyrna varlega is fine even without naming the ball, the opponent, or anything else.

Because varlega is an adverb, not an adjective.

• varlegur = careful, cautious as an adjective
• varlega = carefully, gently, cautiously as an adverb

Here it describes how he tried to kick, so Icelandic uses the adverb:

• Hann var varlegur = He was careful
• Hann spyrndi varlega = He kicked carefully/gently

Dómarinn means the referee or the judge, depending on context. Here it clearly means the referee.

The ending -inn is the suffixed definite article, meaning the. Icelandic usually attaches the to the noun instead of using a separate word:

• dómari = a referee
• dómarinn = the referee

So dómarinn flautaði = the referee whistled.

Both are in the past tense.

• reyna → reyndi = tried
• flauta → flautaði = whistled

These are both weak verbs, and weak verbs often form the past tense with endings like -ði, -di, or -aði.

So the sentence is describing two past actions:

• he tried to kick carefully
• the referee whistled too early

It comes from flauta, which means to whistle. So dómarinn flautaði literally means the referee whistled.

In a sports context, this usually means the referee blew the whistle to stop play, signal a foul, start or end a phase of play, and so on.

No. This of does not mean English of.

In Icelandic, of often means too in the sense of excessively:

• of stór = too big
• of hratt = too fast
• of snemma = too early

So dómarinn flautaði of snemma means the referee whistled too early.

Snemma is an adverb meaning early. Since it describes when the referee whistled, Icelandic uses the adverb form:

• snemma = early
• of snemma = too early

This is similar to English, where early can also function as an adverb.

Because this is the normal neutral order for two main clauses:

• Hann reyndi að spyrna varlega
• en dómarinn flautaði of snemma

Each clause starts with the subject and then the finite verb. That is very natural.

Icelandic is a verb-second language, which means the finite verb tends to come in the second position in main clauses. In this sentence, that happens automatically because the subject is first:

• Hann
  • reyndi
• dómarinn
  • flautaði

So the word order is simple and standard.

En means but here. It connects the two clauses and shows contrast:

• he tried to kick carefully,
• but the referee whistled too early.

This is a very common coordinating conjunction in Icelandic.

Both are in the nominative case because they are the subjects of their clauses.

• Hann = he as subject
• dómarinn = the referee as subject

So:

• Hann reyndi... = He tried...
• dómarinn flautaði... = the referee whistled...

That is why you see the basic subject forms here.