Стоит только перейти рубеж метания, как судья останавливает игру.

Here it is from стоить, not стоять.

So стоит does not mean stands in this sentence. It is part of the fixed expression стоит только + infinitive, which means something like it only takes..., one has only to..., or as soon as....

This is a common Russian construction showing an immediate result.

The basic idea is:

стоит только + infinitive, как + main clause

It means that as soon as the first action happens, the second action happens right away.

In natural English, it often corresponds to:

• as soon as ...
• the moment ...
• all it takes is ... and ...
• one has only to ... for ... to happen

So the sentence presents crossing the line as the trigger, and the referee stopping the game as the automatic consequence.

Только adds the idea of mere sufficiency.

It suggests that this one action alone is enough to trigger the result. In other words, just crossing the line is enough for the referee to stop the game.

Without только, the sentence would still make sense, but the feeling of the mere act of doing this is enough would be weaker.

Because the sentence refers to a completed boundary-crossing event.

Перейти is the perfective infinitive of переходить / перейти, and here that makes sense because the important thing is not the ongoing process of moving, but the moment when the boundary has been crossed.

This is very natural in a rule-like statement:

• once the line is crossed,
• the referee stops the game.

If you used the imperfective переходить, it would sound less natural here, because the sentence is about the completed trigger event.

Russian often leaves the subject unspoken in general statements like this.

The idea is not about one specific named person. It means something like:

• if anyone crosses the throwing line
• if a player crosses the throwing line
• if you cross the throwing line

English usually wants some subject, but Russian can leave it implicit when the meaning is general or obvious from context.

No. Here как does not mean how.

In this sentence, как is part of the construction стоит только ..., как .... It introduces the result clause: the thing that happens immediately after the trigger.

So it functions more like:

• and then
• whereupon
• when immediately

It is also normal to put a comma before как in this structure.

A close alternative is: Стоит только перейти рубеж метания, и судья останавливает игру.

That version is also possible, but как is a very standard choice in this pattern.

Because the sentence describes a regular rule or repeated consequence, not one single future event.

Russian often uses the present tense for:

• general truths
• instructions
• rules
• habitual situations

So судья останавливает игру here means something like:

• the referee stops the game
• the referee will stop the game in such cases
• that is what the referee does

The imperfective останавливает fits this repeated, rule-based meaning very well.

If you used остановит, it would sound more like one specific future occasion rather than a general rule.

Рубеж is the direct object of перейти, so it is in the accusative singular.

However, рубеж is an inanimate masculine noun, and for such nouns the accusative has the same form as the nominative. So you see рубеж, not a visibly different ending.

Метания is genitive singular, dependent on рубеж. It tells you what kind of boundary this is:

• literally the boundary of throwing
• more naturally the throwing line or throwing boundary

So the structure is:

• рубеж = boundary, line
• метания = of throwing

Because останавливать is a transitive verb and takes a direct object.

The noun игра becomes игру in the accusative singular:

• nominative: игра
• accusative: игру

So судья останавливает игру simply means the referee stops the game.

It sounds strongly like a rule, procedure, or standard consequence in a sports context.

That is why several features fit together so well:

• стоит только ... как ... for an immediate trigger-result relationship
• perfective перейти for the completed trigger event
• present imperfective останавливает for a regular, repeated action

So the whole sentence feels like the language of regulations, officiating, or commentary on how the game is supposed to be handled.