What is the subordinate clause in the sentence: "As soon as the doors opened, the crowd pushed into the stadium entrance."?
As soon as.. ... is the subordinate Clause here.
You just keep in mind, and, but, or, nor, semicolon etc are the independent clause connecting words or other all connecting words indicate a dependent or subordinate clause. (A bit exception here that is not so much concern right now as practice will be brought about Confidence)
As soon as the doors opened
A subordinate/dependent clause is a clause that begins with a subordinating conjunction (such as because, that, since, as, etc.) and is not a full sentence.
Independent clauses are full sentences (simple sentences). Dependent/subordinate clauses are not and must be attached to a full sentence.
Examples of subordinate clauses:
until the teacher arrives
after the party ended
In this case, the subordinate clause would be "as soon as the doors opened." After that comes an independent clause, forming a complex sentence.