Ten zawodnik jest silny.

Because zawodnik is a masculine singular noun, and the demonstrative ten must agree with it in gender, number, and case.

• ten = masculine singular
• ta = feminine singular
• to = neuter singular

Since zawodnik is masculine, you say ten zawodnik.

Zawodnik usually means competitor, athlete, player, or contestant, depending on context.

It is a general word for someone who takes part in a sport or competition. For example, in one context it may mean athlete, and in another it may be better translated as player or competitor.

In the present tense, Polish normally does use jest when the sentence means X is Y.

So:

• Ten zawodnik jest silny. = This athlete is strong.

You may sometimes see jest omitted in very informal styles, headlines, or poetic language, but for normal standard speech, jest is the correct form here.

Jest is the 3rd person singular form of the verb być (to be).

Here is the present tense of być:

• jestem = I am
• jesteś = you are
• jest = he/she/it is
• jesteśmy = we are
• jesteście = you are
• są = they are

Since ten zawodnik means this athlete/player and is he in grammatical terms, jest is the correct form.

Because adjectives in Polish must agree with the noun they describe.

Zawodnik is:

• masculine
• singular
• nominative case

So the adjective must also be masculine singular nominative, which is silny.

Compare:

• ten zawodnik jest silny = this male athlete is strong
• ta zawodniczka jest silna = this female athlete is strong
• to dziecko jest silne = this child is strong

Grammatically, yes: zawodnik is a masculine noun and usually refers to a male competitor/athlete.

If you want to refer specifically to a female athlete/competitor, the usual word is:

• zawodniczka

So:

• Ten zawodnik jest silny. = This male athlete is strong.
• Ta zawodniczka jest silna. = This female athlete is strong.

Sometimes masculine forms can be used in broader or generic ways in some contexts, but for a clearly female person, zawodniczka is the natural choice.

It is in the nominative case.

That is because ten zawodnik is the subject of the sentence: it is the person being described.

You can see this in both words:

• ten = masculine singular nominative
• zawodnik = masculine singular nominative

The adjective after jest, silny, is also in nominative here.

Yes. Polish word order is more flexible than English word order.

The neutral, most straightforward version is:

• Ten zawodnik jest silny.

But you might also hear:

• Silny jest ten zawodnik.
• Ten silny zawodnik... if you are using the adjective directly before the noun in a different sentence structure

Changing the order can affect emphasis rather than basic meaning. For a learner, the given order is the safest and most natural starting point.

Both can refer to a sports person, but they are not exactly the same.

• zawodnik = competitor, player, contestant, athlete in a competition
• sportowiec = sportsman, athlete, someone who does sport more generally

So zawodnik often emphasizes participation in a specific event, match, or competition, while sportowiec can sound broader.

A rough English-friendly guide is:

• ten → like ten
• zawodnik → za-VOD-neek
• jest → roughly yest
• silny → roughly SEEL-nih

A few helpful pronunciation notes:

• Polish j sounds like English y
• Polish w sounds like English v
• Polish y is a vowel that does not exist exactly in English; in silny, it is not the same as ee

The stress is usually on the second-to-last syllable:

• za-VOD-nik
• SIL-ny

Sometimes, depending on context.

Polish ten/ta/to often covers uses that English splits between this and that. In many beginner sentences, ten is translated as this, but in real usage it can also work more like that, especially when context makes the reference clear.

So:

• Ten zawodnik jest silny. can often be understood as This athlete is strong
• but in some situations it might be closer to That athlete is strong

If you need a stronger contrast like this one here versus that one there, Polish can express that more explicitly with context or extra words.

Usually in this sentence, yes, it most naturally means physically strong.

But silny can also mean strong in a broader sense, depending on context, for example:

• silny charakter = strong character
• silny argument = strong argument
• silny wiatr = strong wind

In Ten zawodnik jest silny, the most likely meaning is that the athlete is physically strong.