Should I use "was" or "were" in the following context?
A huge crowd were/was present there.
Was is preferable in this particular example, and in general with the word crowd. However, due to the phenomenon of "notional agreement", plural agreement is also possible in principle with the word crowd, and may sound acceptable in some circumstances (acceptability judgments for specific examples are likely to differ between speakers).
In general, collective nouns can take either singular agreement, according to their form, or plural agreement, according to their sense. This basic principle is mentioned by the answers to the following question (Are collective nouns always plural, or are certain ones singular?) along with some generalizations that may be helpful. (I do think it is good to remember that verb agreement with collective nouns often tends to be different on different sides of the Atlantic, but I think this is often stated as too much of an absolute. I'm an American English speaker, and I feel like the situation is more complicated than "singular agreement in American English, plural agreement in British English"; I've heard the same from British English speakers, and British English guides often say that either singular or plural agreement can be used, sometimes with subtle differences in implied meaning.)
The word crowd seems to rarely take plural agreement, even in dialects where notional agreement is common for some other collective nouns. The Google Ngram Viewer shows the expected difference between British and American English, but it is relatively small:
The frequency of "crowd are" may even be an exaggeration of the frequency of true plural agreement with the word "crowd", since I think this chart picks up false positives like "the individuals in the crowd are...".
So in general, as a writer, you'll be safe if you use singular agreement.
However, you may encounter plural agreement with the word "crowd" in things that you read, and it is not necessarily an error.
Here are links to discussions of this topic on other websites:
Here are some examples I found on Google Books of plural agreement with the word "crowd":
"After the deluge," when "our crowd" are out of office and scattered, the anti- Washington crowd here will be sure to secure the influence of The Bee.
Ralph Waldo Tyler to Emmett Jay Scott, Washington D.C., Dec. 11, 1912 in Booker T. Washington Papers Volume 12: 1912-14, edited by Louis R. Harlan and Raymond W. Smock
A crowd of workpeople will be required all at once to pick up the sheaves, or to cart them to the rick; and the difference will lie in this, that while now the crowd are employed, say twelve hours, then they will be employed only nine.
Hodge and His Masters, by Richard Jefferies (p. 268)
This happens everywhere The Cure go, but the Chicago crowd are going to be luckier than most—depending on how sociable the band are or aren't feeling after a show, the tour bus is often sent off empty, while Smith and company are spirited away in anonymous, windowless minibuses.
Rock and Hard Places: Travels to Backstages, Frontlines and Assorted Sideshows, by Andrew Mueller (p. 79)
You are in the area of the world now known as Southern Mexico and Guatemala, and the roaring crowd are all Mayan—an Indian people famed for their buildings, astronomy, and ball games.
The crowd were more violent than on the previous occasion, and he repeated that they began the attack on the emergency men, and then the police interfered.
"Tithe Disturbances in North Wales", in Hansard's Parliamentary Debates, Third Series, Vol 326, 1888
Since I'm an American English speaker, and I haven't thought about this before, I can't precisely describe when "crowd" can take notional plural agreement. However, I would say based on the above examples that plural agreement is made more likely by the following circumstances:
a preceding definite article: "the [..] crowd" seems more likely to be treated as plural than "a crowd"
a following "of [plural noun]", or maybe even just proximity to "a crowd of..." (as in the second example)
use of a plural pronoun like "them" or "themselves" to refer to the crowd later in the sentence (this factor is mentioned in the linked UsingEnglish and WordReference threads)
use of the word in the sense that Collins gives second, as "a group of friends, or a set of people who share the same interests or job [informal]". Collins' example sentence for this definition shows plural agreement:
All the old crowd have come out for this occasion.
I would say that plural agreement seems fairly infelicitous in your sentence because none of these circumstances apply.
Discussion in comments have led me to adjust my answer (for posterity; current downvotes are fair and this answer should probably not be the accepted one). Which form is grammatically correct is unclear, to the extent that it may be that neither is correct or incorrect. So no ruling on which is more correct, by any standard, from me.
As for what you should use, in the U.S. was is far more common in my region (the Midwest), though neither would be unfamiliar. Someone might attempt to correct you if you use were, whether or not that correction is valid, and I have never encountered someone correcting from was.
Crowd is a singular noun, and so the verb is conjugated accordingly.