There was/were only a handful

Was . . . a handful of spectators was at the match--singular.

Were. A "handful" is a small number. Whenever you have a subject noun followed by a prepositional phrase, the verb should modify the subject noun, not the object of the preposition, *but* that's not always the case. When "number" is preceded by "the," "number" is singular and takes the singular verb. When "number" is preceded by "a," "number" is plural and takes a plural verb. Therefore I would use "were".

there was a handful of candy

there were handfuls of candy

I'm going with were as the proper form here.
You can reduce the sentence and see that were is the proper use with the plural spectators.

There were spectators at the soccer match.
There were only a handful of spectators................

handful - singular

was

there was a handful of spectators

there were only four spectators

Interesting dilemma here.
The spectators at the soccer match were only a handful.
There were only a few spectators at the soccer match.

Handful may be may be one of those words that is singular or plural by context.
Hmmmm.
There were a handful of other options available
There was a handful of other options available

Yes, I agree, and surely in this context the phrase "a handful" does not mean a literal handful - you can't get your hand around one person let alone more than one - it is a metaphor and means "a small number" which is why I think "were" is the right option.

That's what I'm thinking.
In this context, handful is a nonspecific plural, same as a few.

Just curious to know whether it should be ...'that are singular or plural ...'

I think it probably should be are rather than is.

There was a ton of replies to this, wasn't there?

There were a lot of responses.