Mijn spatbord zit los, waardoor mijn broek vies wordt.

Spatbord literally means a mudguard or fender. In this sentence, it most likely refers to the part on a bicycle that protects you from water and mud splashing up from the wheel.

• spat = splash
• bord = board/panel

So it is the part that stops splashes.

In Dutch, zitten is often used for the way something is positioned, attached, or fixed.

So:

• Mijn spatbord zit los = My mudguard is loose

This is very natural Dutch. English often just says is loose, but Dutch commonly says zit los for something that is attached but not firmly.

Other examples:

• De knop zit vast = The button is stuck / fixed
• Het handvat zit los = The handle is loose

Waardoor means as a result of which, which causes, or more naturally in English, so that, thereby, or because of that depending on context.

In this sentence:

• Mijn spatbord zit los, waardoor mijn broek vies wordt.
• My mudguard is loose, which causes my trousers to get dirty.

It connects the first situation to its consequence.

A useful way to think about it:

• waardoor = by which / because of which / as a result of which

Because waardoor introduces a subordinate clause.

In Dutch subordinate clauses, the conjugated verb usually goes to the end:

• mijn broek vies wordt

Compare:

• Main clause: Mijn broek wordt vies.
• Subordinate clause: ... waardoor mijn broek vies wordt.

This verb-final word order is one of the most important patterns in Dutch grammar.

Because the subject is mijn broek, which is singular.

• mijn broek = my trousers/pants

Even though English trousers/pants can look plural in meaning, Dutch broek is a singular noun.

So:

• mijn broek wordt vies = my trousers get dirty

If the subject were plural, you would use worden:

• mijn schoenen worden vies = my shoes get dirty

It can mean either, depending on the variety of English you are using.

• In British English: usually trousers
• In American English: usually pants

So mijn broek is my trousers or my pants.

Vies is the basic predicate adjective form, used after verbs like zijn, worden, blijven.

Here it comes after wordt:

• mijn broek wordt vies = my trousers get dirty

Vuile is the inflected form used before a noun:

• een vuile broek = dirty trousers / dirty pants
• de vuile broek = the dirty trousers / pants

So:

• De broek is vies ✅
• Een vieze / vuile broek ✅

Both can relate to dirty, but they are not always used in exactly the same way.

• vies often means dirty, filthy, or even nasty
• vuil also means dirty, but can sound a bit more neutral or physical in some contexts

In everyday speech, vies worden is extremely common for getting dirty.

So in this sentence, vies is very natural:

• mijn broek vies wordt = my trousers get dirty

Because Dutch normally repeats the possessive adjective with each noun if both belong to the same person.

• Mijn spatbord ... mijn broek

English does the same in many cases:

• My mudguard is loose, so my trousers get dirty.

You would not normally omit the second mijn in Dutch.

Yes. A learner might also see:

• Mijn spatbord zit los, dus mijn broek wordt vies.

This means almost the same thing:

• My mudguard is loose, so my trousers get dirty.

The difference is mainly style:

• dus = simpler, more direct, very common
• waardoor = a bit more formal or more tightly linked as cause and result

Both are correct, but waardoor gives the sentence a slightly more connected, explanatory feel.

Yes. This is very common in Dutch.

Dutch often uses zitten for parts that are attached, located, stuck, loose, or fixed:

• Het wiel zit scheef. = The wheel is crooked.
• De deurklink zit los. = The door handle is loose.
• Er zit een gat in mijn jas. = There is a hole in my coat.

This is broader than English sit, so learners often need time to get used to it.

A rough guide for English speakers:

• Mijn ≈ mine
• spatbord ≈ spaht-bort
• zit los ≈ zit lohs
• waardoor ≈ vahr-door
• mijn broek ≈ mine brookh
• vies wordt ≈ veess vurt

A few pronunciation notes:

• g in broek is not present, but oe sounds like oo in boot
• ui is not in this sentence, so that helps
• wordt is pronounced more simply than it looks; the final d is not strongly pronounced in connected speech

A natural rhythm would be:

Mijn SPAT-bord zit LOS, waarDOOR mijn BROEK vies wordt.