Der Mitspieler kommt zum Spieleabend.

Because Mitspieler is the subject of the sentence—the person doing the action of coming. In German, a masculine noun in the nominative singular takes der.

So:

• der Mitspieler = nominative, masculine, singular
• it means the fellow player / teammate / other player, depending on context

If it were in a different case, the article would change, for example:

• den Mitspieler = accusative
• dem Mitspieler = dative

Mitspieler is a compound noun:

• mit- = with / fellow-
• Spieler = player

So Mitspieler literally means fellow player, teammate, or another player, depending on the situation.

German often makes new words by combining smaller words into one noun, and this is a very common pattern.

Because the subject is third-person singular: der Mitspieler = he / the player.

The verb kommen is conjugated like this in the present tense:

• ich komme
• du kommst
• er/sie/es kommt
• wir kommen
• ihr kommt
• sie/Sie kommen

Since der Mitspieler is singular, the correct form is kommt.

Zum is a contraction of:

• zu dem → zum

So:

• zum Spieleabend = to the game night

This contraction is very common in German.

Compare:

• zu dem Park → zum Park
• zu der Schule → usually zur Schule

So zum is used for zu + dem.

Because the preposition zu takes the dative case.

So the noun phrase after zu must be in the dative:

• nominative: der Spieleabend
• dative: dem Spieleabend

Then zu dem becomes zum.

So the structure is:

• Der Mitspieler = nominative subject
• kommt = verb
• zum Spieleabend = prepositional phrase with dative

Because German very often combines nouns into compound nouns.

Here:

• Spiel = game
• Abend = evening

In the compound, it becomes Spieleabend, often understood as game night or games evening.

The -e- in the middle is a linking element. These linking sounds are common in German compounds and are not always directly predictable from English.

Also, like all German nouns, Spieleabend is capitalized.

Because in German, all nouns are capitalized.

So in this sentence:

• Mitspieler is a noun
• Spieleabend is a noun

That is why both begin with capital letters.

This is one of the most noticeable spelling differences between German and English.

It is the normal word order for a basic German main clause:

• Subject + verb + other information

So:

• Der Mitspieler = subject
• kommt = verb
• zum Spieleabend = destination / event phrase

German main clauses usually put the conjugated verb in the second position. Here, the subject is first, so the verb comes right after it.

You could also move another element to the front for emphasis, but then the verb still stays in second position:

• Zum Spieleabend kommt der Mitspieler.

That is grammatical too, but it changes the emphasis.

Formally, kommt is present tense. But in German, the present tense is often used to talk about the near future as well, especially when the context makes it clear.

So this sentence can mean something like:

• The fellow player is coming to the game night
• or The fellow player comes to the game night

Depending on context, English may translate it with a future-like meaning even though German uses the present tense.

Because German uses different prepositions depending on the kind of relationship being expressed.

Zu is commonly used for:

• going to a person
• going to an event
• going to certain destinations

A Spieleabend is an event, so zu is natural here:

• zum Spieleabend

Using in would suggest going physically into something like a room, building, or enclosed space, which is not the idea here.

So the sentence is focusing on attending the event, not entering a space.

Grammatically, Mitspieler is a masculine noun, and in many contexts it refers to a male person.

If you want to refer specifically to a female player, you would usually say:

• die Mitspielerin

If you want to speak in a gender-inclusive way, modern German offers several possibilities depending on style and context, for example:

• Mitspieler und Mitspielerinnen
• Mitspielende

But in this sentence, der Mitspieler is the standard masculine singular form.

Yes, but it is not exactly the same.

• der Spieler = the player
• der Mitspieler = the fellow player / teammate / co-player

Mitspieler adds the idea that this person is one of the other participants or someone playing with others. Spieler is more general.

So both can be correct, but Mitspieler is a bit more specific.