Úder není ani forhend, ani bekhend.

It means neither ... nor.

So:

• ani forhend, ani bekhend = neither a forehand nor a backhand

This is the normal Czech way to join two negative alternatives. English uses neither ... nor; Czech uses ani ... ani.

Because Czech normally repeats it before each item:

• ani X, ani Y = neither X nor Y

So Úder není ani forhend, ani bekhend is literally structured like:

• The stroke is not neither-forehand, neither-backhand
• natural English: The stroke is neither a forehand nor a backhand

Using ani only once would not sound right here.

Není is the 3rd person singular form of být (to be) in the present tense, with negation:

• je = is
• není = is not

It is singular because the subject úder is singular:

• Úder není ... = The stroke is not ...

Úder is a masculine inanimate noun meaning something like stroke, hit, or shot, depending on context.

In this sentence it is in the nominative singular because it is the subject:

• Úder = the stroke / the shot

So the basic structure is:

• Úder = subject
• není = verb
• ani forhend, ani bekhend = what it is not

Because Czech has no articles.

English needs words like a, an, and the, but Czech usually expresses definiteness from context. So:

• Úder can mean a stroke, the stroke, or just stroke
• forhend can mean a forehand
• bekhend can mean a backhand

The exact English article depends on the situation, not on a separate Czech word.

They are in the nominative singular.

That may feel surprising to an English speaker, because after to be Czech sometimes uses different patterns. But here the nouns are being used as labels or categories:

• forhend = forehand
• bekhend = backhand

So the sentence is classifying the stroke: it is not one category and not the other category.

Good question. After být (to be), Czech can use either nominative or instrumental in different situations.

Here, nominative is natural because the sentence is giving a classification/label:

• It is not a forehand, not a backhand.

Using the instrumental here would sound less natural for this kind of sports labeling. The nominative fits the idea of naming shot types.

So this sentence is best understood as:

• This stroke is neither a forehand nor a backhand.

Yes, they are common loanwords in Czech sports language, borrowed from English forehand and backhand but adapted to Czech spelling:

• forehand → forhend
• backhand → bekhend

This kind of spelling adaptation is very common in Czech, especially in sport and technology.

Approximately like this:

• forhend ≈ FOR-hent
• bekhend ≈ BEK-hent

A few useful points:

• stress in Czech is normally on the first syllable
• final d is often pronounced more like t in actual speech

So even though they come from English, they sound Czech in pronunciation.

Yes, Czech word order is fairly flexible, but the original sentence is a neutral, natural order:

• Úder není ani forhend, ani bekhend.

You could change the order for emphasis, for example if you wanted to highlight the contrast, but the given version is the straightforward one.

So for a learner, this is the best pattern to remember:

• X není ani A, ani B.
• X is neither A nor B.

Yes. A very useful pattern is:

• [noun] není ani [A], ani [B].
• [noun] is neither [A] nor [B].

Examples:

• To není ani pravda, ani lež.
  It is neither truth nor a lie.

• On není ani učitel, ani student.
  He is neither a teacher nor a student.

• To není ani levné, ani drahé.
  It is neither cheap nor expensive.

So this sentence is a good model for making neither ... nor statements in Czech.