The adjectival subordinate clause in this sentence is “that tried charging at us.”
A subordinate clause is a dependent clause, that is, not a complete sentence, but still provides extra information in the sentence.
Subordinate clauses are introduced by subordinate conjunctions or relative .
In this sentence, we see the word that, which is a subordinate conjunction. The word that precedes the rest of the thought,
that tried charging back at us
This is the sentence’s subordinate clause. It is dependent, and provides additional information in the sentence. In fact, the sentence could stand alone without the subordinate clause, it just wouldn’t be as descriptive:
The bull is back in the pen.
However, the subordinate clause gives the sentence context. (Why is the bull back in the pen? Had it escaped?)
The bull that tried charging at us is back in the pen.
Since the subordinate clause describes the bull, which is a noun, it is function as an adjective, since adjectives modify .