אל תתחילו את המשחק בלי שהמאמן יגיע.

אל is the normal word for a negative command or prohibition: don’t ...

So אל תתחילו means don’t start.

By contrast, לא usually just negates a statement:

• אתם לא מתחילים = you are not starting

In other words:

• אל תתחילו = command
• לא מתחילים = statement

In Hebrew, negative commands are usually made with אל + future form.

So even though תתחילו is formally a future form, in אל תתחילו it means don’t start, not you will start.

Compare:

• תתחילו = you will start
• אל תתחילו = don’t start

For a positive command, Hebrew can use the imperative:

• התחילו! = Start!

תתחילו is second person plural: you all / you guys / you two+.

So the speaker is talking to more than one person.

Related forms:

• אל תתחיל = don’t start (to one male)
• אל תתחילי = don’t start (to one female)
• אל תתחילו = don’t start (to a group)

Because they come from two different parts of the verb form.

• The first ת marks second person / future
• The second ת is part of the verb stem from להתחיל

So the form is built roughly like this:

• להתחיל = to start
• stem: תחיל
• add future/2nd-person prefix ת־
• add plural ending ־ו

Result: תתחילו

So the double ת is completely normal.

את is the Hebrew direct object marker. It appears before a definite direct object.

Here, המשחק means the game, which is definite, so Hebrew uses את:

• את המשחק = the game as the direct object

It usually does not get translated into English.

Compare:

• להתחיל משחק = start a game
• להתחיל את המשחק = start the game

Because המאמן is not the direct object there. It is the subject of the verb יגיע.

In שהמאמן יגיע:

• המאמן = the coach
• יגיע = will arrive

So the coach is the one doing the arriving. That is why there is no את.

Here ש־ introduces a subordinate clause.

After בלי, Hebrew often uses ש־ when a whole clause follows:

• בלי המאמן = without the coach
• בלי שהמאמן יגיע = without the coach arriving / before the coach arrives

So ש־ is what allows בלי to be followed by a full mini-sentence, not just a noun.

Because the coach’s arrival has not happened yet at the time of the command.

Hebrew often uses the future in subordinate clauses when the event is still in the future:

• עד שהמאמן יגיע
• לפני שהוא יגיע
• בלי שהמאמן יגיע

English often uses a present form in similar cases, such as until the coach arrives, but Hebrew normally uses the future.

Because the meaning is slightly different.

• בלי המאמן = without the coach
• בלי שהמאמן יגיע = without the coach arriving / before the coach arrives

The version with יגיע focuses on the event of arrival, not just the coach’s presence in general.

So this sentence is not only saying don’t start without him; it is specifically tying the start of the game to the moment when he arrives.

They are very close, but not exactly the same.

• עד שהמאמן יגיע = until the coach arrives
• בלי שהמאמן יגיע = without the coach arriving / before the coach arrives

In many real situations, both could work. But the nuance is different:

• עד ש־ focuses on waiting until a point in time
• בלי ש־ focuses on not doing something unless that event has happened

If you want the most direct equivalent of Don’t start the game until the coach arrives, then אל תתחילו את המשחק עד שהמאמן יגיע is especially straightforward.

It specifically suggests that his arrival has not happened yet.

That comes from the verb יגיע = will arrive.

So the emphasis is on arrival, not merely absence. If you only wanted to say Don’t start the game without the coach, Hebrew could say:

אל תתחילו את המשחק בלי המאמן

That version does not focus on the act of arriving.