Úder může být forhend nebo bekhend.

Because Czech, like English, uses a modal verb plus an infinitive.

• může = can / may / is able to
• být = to be

So může být literally means can be.

This is completely normal Czech structure:

• může přijít = can come
• může hrát = can play
• může být = can be

Může is the 3rd person singular form of moci (to be able to / can).

It is může because the subject is úder, which is singular:

• úder může být... = the stroke can be...

If the subject were plural, you would use mohou:

• Údery mohou být forhend nebo bekhend. = Strokes can be forehand or backhand.

So the verb agrees with úder.

Úder is in the nominative singular, because it is the subject of the sentence.

Basic breakdown:

• úder = subject
• může být = verb phrase
• forhend nebo bekhend = what the subject can be

Also, úder is a masculine inanimate noun.

Because after být (to be), Czech often uses the nominative for predicate nouns.

So:

• Úder je forhend.
• Úder může být forhend nebo bekhend.

Here forhend and bekhend are naming what the stroke is, so the basic nominative form is natural.

This is similar to:

• To je problém. = That is a problem.
• On je učitel. = He is a teacher.

They are standard Czech spellings of English loanwords:

• forhend < forehand
• bekhend < backhand

Czech often adapts foreign sports terms to Czech spelling, especially when they are common.

So although they come from English originally, in this sentence they function as normal Czech nouns.

Yes, they can.

They are usually treated as masculine inanimate nouns, so they can take Czech endings when needed. For example:

• nominative: forhend
• genitive: forhendu
• instrumental: forhendem

And similarly:

• bekhend
• bekhendu
• bekhendem

In your sentence, they stay in the basic form because nominative is needed.

Because Czech has no articles.

English says:

• a stroke
• the stroke

Czech just says:

• úder

You understand whether it means a stroke, the stroke, or stroke from context.

That is very normal in Czech and often feels strange at first for English speakers.

Yes, Czech word order is fairly flexible, but not every order sounds equally natural.

The given sentence:

• Úder může být forhend nebo bekhend.

is a very normal neutral order.

You could also hear:

• Úder může být bekhend nebo forhend.

That only changes the order of the two options.

A more marked order is possible in the right context, but the original sentence is the safest and most natural for a learner.

A simple pronunciation guide:

• Úder ≈ OO-der
• může ≈ MOO-zhe
• být ≈ beet
• forhend ≈ FOR-hent
• nebo ≈ NE-bo
• bekhend ≈ BEK-hent

A few useful points:

• ú is a long u
• ž sounds like the s in vision
• ý is a long ee sound
• Czech stress is usually on the first syllable of each word

So the rhythm is roughly:

Ú-der | MŮ-že | BÝT | FOR-hend | NE-bo | BEK-hend

Je means is, while může být means can be / may be.

So:

• Úder je forhend. = The stroke is a forehand.
• Úder může být forhend nebo bekhend. = A stroke can be a forehand or a backhand.

The sentence with může být expresses possibility, classification, or one option among others, not a definite statement about one specific stroke.