On a warm August evening on a pier in Cherry Grove, New York, I watched a display of fireworks. The wooden dock was crowded, everyone excited for the show to start. Police boats and fire boats whizzed around on the water.
This construction is perfectly grammatical, although it is often positioned at the beginning of the sentence, to stress its role of explaining why people crowded the dock. Then positioned at the end of the sentence, it could have less of this "explaining" power, and be more "descriptive". As a non-native speaker, I'm not sure.
It is called an "absolute construction".
An absolute construction has no syntactic link to the main clause, but it is subordinate in form. In our case, it is a past-participle clause: the word "excited" is a past participle.
If you use and and add the finite verb was, you will have turned the clause into a finite clause
The wooden dock was crowded and everyone was excited for the show to start.
...here we have two finite clauses which state two separate facts. Each clause is independent of the other clause, while in the original text the second clause is semantically dependent upon the first.
A broader term, used by Huddleston and Pullum, is "supplement". Sometimes a supplement misses a subject and its missing subject is controlled by the subject in the main clause:
Excited for the show to start, people crowded the wooden dock.
..here the link between the two clauses is stronger, because the supplement has no subject of its own (like "everyone"), and we understand that it's the "people" who were "excited for the show to start".