Правонарушитель признал ошибку.

Because ошибку is in the accusative case.

In this sentence, ошибка is the direct object of признал: it is the thing the offender admitted.
For most feminine nouns ending in -а, the accusative singular changes -а to -у:

• ошибка = mistake/error
• ошибку = mistake/error, as the direct object

So:

• Правонарушитель признал ошибку. = The offender admitted the mistake.

Признал is the past tense, masculine singular form of the verb признать.

It tells you three things:

• past tense: the action happened in the past
• masculine: the subject is grammatically masculine
• singular: there is one subject

Russian past tense forms agree with the subject in gender and number:

• он признал = he admitted
• она признала = she admitted
• оно признало = it admitted
• они признали = they admitted

Since правонарушитель is a masculine singular noun, признал matches it.

This is a question of aspect, which is very important in Russian.

• признать → perfective
• признавать → imperfective

Here, признал is perfective, so it presents the action as completed: the offender admitted it, and that admission happened as a single finished event.

By contrast, признавал would usually suggest something like:

• he was admitting it
• he used to admit it
• he admitted it repeatedly
• the focus is on the process rather than the completed result

In Правонарушитель признал ошибку, the perfective is natural because the sentence reports a completed fact.

It is in the nominative case, because it is the subject of the sentence.

The subject is the person who performs the action:

• правонарушитель = the offender / violator
• признал = admitted
• ошибку = the mistake

So the structure is:

• правонарушитель = subject, nominative
• ошибку = direct object, accusative

Not always. Признать has a few related meanings, and context matters.

Common meanings include:

• to admit / acknowledge
  
  • признать ошибку = to admit a mistake
• to recognize
  
  • признать кого-то = to recognize someone
• to declare / to accept officially in some contexts
  
  • признать виновным = to find guilty
  • признать законным = to declare lawful

In this sentence, признал ошибку clearly means admitted a mistake/error, not recognized.

It is a real and useful word, but it sounds formal and often legal/official.

Правонарушитель means someone who committed an offense or violation. You will often see it in:

• legal texts
• police reports
• official statements
• news reports

In everyday speech, people might use something less formal depending on context, such as:

• человек = person
• виновник = the person at fault / culprit
• нарушитель = violator, offender

So this sentence has a somewhat official tone.

Because Russian has no articles like a or the.

Russian simply says:

• Правонарушитель признал ошибку.

Depending on context, English might translate this as:

• The offender admitted the mistake.
• An offender admitted a mistake.
• The offender admitted a mistake.

The exact choice in English depends on context, but Russian does not mark that difference with articles.

Yes. Russian word order is more flexible than English word order because case endings show grammatical roles.

The neutral order here is:

• Правонарушитель признал ошибку.

But other orders are possible for emphasis, for example:

• Ошибку признал правонарушитель.
  Emphasis on the mistake
• Признал ошибку правонарушитель.
  More marked; can sound like narrative or contrastive emphasis

Even when the order changes, the cases still show who did what:

• правонарушитель is still the subject
• ошибку is still the object

Grammatically, the sentence is treated as masculine singular because of the noun правонарушитель and the verb form признал.

A few important points:

1. Правонарушитель is a masculine noun.
2. The past tense verb agrees with it: признал is masculine singular.
3. In Russian, masculine nouns for roles or professions are often used as dictionary forms.

So grammatically, this sentence is masculine. In real life, if the offender were explicitly female, Russian might use a different wording or keep the role noun but make agreement choices depending on style and context.

For a learner, the key takeaway is:

• признал = masculine singular past
• that matches правонарушитель

The stress is:

• правонаруши́тель
• призна́л
• оши́бку

A rough pronunciation guide:

• пра-ва-на-ру-ШИ-тель
• приз-НАЛ
• а-ШИБ-ку

Stress matters in Russian, so it is worth learning words together with their stress.

Yes. Ошибка can mean both mistake and error, depending on context.

• In everyday speech, mistake is often the most natural translation.
• In technical or formal contexts, error may fit better.

So признал ошибку could be understood as:

• admitted a mistake
• admitted an error

The best English choice depends on the situation.