Nie krzycz na psa, on i tak się boi.

Because Nie krzycz is the negative imperative: Don’t shout.

• krzyczysz = you are shouting / you shout
• krzycz = shout!
• nie krzycz = don’t shout!

So the sentence is giving an instruction or warning, not describing what someone is doing.

Krzycz is the 2nd person singular imperative of krzyczeć (to shout / to yell).

It is used when speaking to one person informally, like English you in Don’t shout at the dog.

Related forms:

• krzycz! = shout!
• nie krzycz! = don’t shout!
• krzyczcie! = shout! (to more than one person, or sometimes informal plural)
• nie krzyczcie! = don’t shout!

In Polish, krzyczeć na kogoś / na coś means to shout at someone / something.

So:

• krzyczeć = to shout
• krzyczeć na psa = to shout at the dog

This is just the pattern the verb uses. English speakers often want to translate word-for-word, but here Polish requires na.

Examples:

• Nie krzycz na dziecko. = Don’t shout at the child.
• Krzyczał na mnie. = He shouted at me.

Because after na in the pattern krzyczeć na kogoś / coś, Polish uses the accusative case.

The noun pies (dog) changes in the accusative singular:

• nominative: pies
• accusative: psa

So:

• pies = the dog (subject form)
• na psa = at the dog

This is a very common kind of case change in Polish.

Here i tak means something like:

• anyway
• as it is
• already
• in any case

So on i tak się boi means the dog is already afraid / afraid anyway, so shouting makes no sense.

Important: i tak is an expression. It is not understood literally as and yes.

Examples:

• Nie idź tam, i tak jest zamknięte. = Don’t go there, it’s փակ anyway.
• Nie tłumacz, i tak nie uwierzy. = Don’t explain, he won’t believe it anyway.

Yes, it could be omitted.

Polish often leaves out subject pronouns when they are clear from the verb:

• Nie krzycz na psa, i tak się boi.

This is perfectly natural.

The version with on:

• Nie krzycz na psa, on i tak się boi.

adds a bit of clarity or emphasis, roughly like he’s scared anyway. It helps point back to the dog.

So both are possible, but on is not required just because English uses he.

Because on is the subject pronoun: he.

In this clause, the dog is the one who is afraid, so we need the subject form:

• on = he

jego usually means:

• him
• his

So jego i tak się boi would not work here as the subject.

Się is part of the verb bać się, which means to be afraid / to fear.

So the basic dictionary form is:

• bać się = to be afraid

This does not literally mean to fear oneself in normal use. For learners, it is best treated as a single verb that simply requires się.

Examples:

• Boję się. = I’m afraid.
• On się boi. = He is afraid.
• Dzieci się boją. = The children are afraid.

Yes, both are possible:

• on i tak się boi
• on i tak boi się

But on i tak się boi sounds more natural here.

In Polish, word order is more flexible than in English, and short words like się often move around depending on rhythm, emphasis, and style.

A useful beginner rule is:

• learn the verb as bać się
• accept that in sentences you may see both boi się and się boi

Yes. Bać się usually takes the genitive.

Examples:

• boić się psa = to be afraid of the dog
• boić się ciemności = to be afraid of the dark
• boić się ludzi = to be afraid of people

In your sentence, there is no extra noun after boi, because the idea is simply he is afraid / he’s scared.

Because the sentence contains two clauses:

• Nie krzycz na psa
• on i tak się boi

In Polish, it is normal to separate such clauses with a comma.

So the comma works much like in English:

• Don’t shout at the dog, he’s scared anyway.

Usually, yes. Krzyczeć na kogoś normally means to yell at someone, so it sounds negative, angry, or scolding.

If you just want to say someone is shouting in someone’s direction or calling loudly, Polish may use other wording depending on context.

So in this sentence, Nie krzycz na psa clearly means Don’t yell at the dog.

It is talking to one person informally, because of krzycz.

If you were speaking to more than one person, you would say:

• Nie krzyczcie na psa, on i tak się boi.

If you wanted a more formal singular form, Polish would normally rephrase it depending on the level of politeness, for example with proszę:

• Proszę nie krzyczeć na psa, on i tak się boi.

So the original sentence sounds direct and natural when speaking to one person.