W dobrej drużynie powinno się słuchać trenera i pomagać w obronie.

Because after w meaning in, Polish normally uses the locative case.

So:

• drużyna = team
• w drużynie = in a team

The adjective has to match the noun, so:

• dobra drużyna = a good team
• w dobrej drużynie = in a good team

Both the noun and the adjective change form:

• dobra → dobrej
• drużyna → drużynie

Powinno się is an impersonal way to say one should, people should, or it is proper to.

So:

• Powinno się słuchać trenera = One should listen to the coach
• Powinno się pomagać w obronie = One should help in defense

This structure is very common in Polish when talking about general rules, habits, or expectations, without naming a specific person.

Compare:

• Powinieneś słuchać trenera = You should listen to the coach
• Powinno się słuchać trenera = One should listen to the coach / People should listen to the coach

The verb słuchać usually takes the genitive case, not the accusative.

So:

• trener = coach
• trenera = of the coach / coach (genitive form)

That is why Polish says:

• słuchać trenera = to listen to the coach

This is something English speakers often have to memorize, because English listen to does not work the same way grammatically.

A few similar examples:

• słuchać muzyki = to listen to music
• słuchać rodziców = to listen to one’s parents

Because after powinno się, Polish commonly uses the infinitive.

So the pattern is:

• powinno się + infinitive

Examples:

• Powinno się ćwiczyć. = One should exercise.
• Powinno się odpoczywać. = One should rest.
• Powinno się słuchać trenera. = One should listen to the coach.

That is why you see:

• słuchać
• pomagać

rather than conjugated forms.

Here się helps create the impersonal meaning.

Without it, the sentence would not have the same natural general rule feeling.
With się, Polish expresses something like:

• it is done
• people do
• one should

So powinno się is not literally reflexive in the English sense. It is just part of a very common Polish structure.

W obronie means in defense or on defense, depending on context.

• obrona = defense
• w obronie = in defense

Again, w here requires the locative case, so:

• obrona → obronie

In a sports context, pomagać w obronie means:

• to help defensively
• to help out in defense
• to contribute when defending

Because Polish often expresses relationships through case endings instead of prepositions.

In English:

• listen to the coach

In Polish:

• słuchać trenera

The verb słuchać itself requires the right case form, so no separate word like to is needed here.

This is a major difference between English and Polish:

• English often uses prepositions
• Polish often uses case endings

Yes. Należy słuchać trenera is also correct and means something like one should listen to the coach or it is necessary/proper to listen to the coach.

The difference is mostly tone:

• powinno się = should, more general and natural in everyday statements
• należy = should / ought to / it is necessary to, often a bit more formal

So both work, but powinno się sounds very natural in a sentence about good team behavior.

In this sentence, trenera comes from trener, which is grammatically masculine.

In real usage, Polish often still uses trener for a coach regardless of gender, especially in sports contexts, though trenerka can also be used for a female coach in some contexts.

So you may hear:

• słuchać trenera
• słuchać trenerki

depending on the speaker and situation.

Yes, Polish word order is fairly flexible, though some orders sound more natural than others.

The given sentence:

• W dobrej drużynie powinno się słuchać trenera i pomagać w obronie.

is very natural.

You could also say:

• Powinno się w dobrej drużynie słuchać trenera i pomagać w obronie.

But that sounds less smooth and less standard.

Putting W dobrej drużynie first works well because it sets the scene: in a good team...

Because these mean different things.

• pomagać w obronie = to help in defense / while defending
• pomagać obronie = to help the defense

The version in your sentence focuses on the activity or area: defense as part of play.

So w obronie is the natural phrase in a sports context when you mean someone should contribute defensively.