Learn Portuguese (Portugal): Mal os vi chorar nos bastidores, adiei a estreia. - As soon as I saw them cry backstage, I postponed the premiere.

Two rules are working together here. First, with perception verbs like ver (to see), the object pronoun moves up to associate with the main verb rather than the infinitive—a process called clitic climbing. Second, the conjunction Mal (as soon as) is a "magnet" word that triggers proclisis, pulling the pronoun to the very front of the verb phrase. This gives us os vi chorar instead of vi-os chorar.

Since os is plural, could I use the personal infinitive and say os vi chorarem?

Generally, no. When you use a clitic pronoun (like os, as, nos) as the object of a perception verb, the following infinitive stays in its basic, uninflected form (chorar). You would only use the personal infinitive here if you used a full noun phrase instead of a pronoun, such as vi os atores chorarem (I saw the actors cry).

I learned that mal means "bad" or "badly". How does it mean "as soon as" in this sentence?

When mal is used to connect two clauses (acting as a conjunction rather than an adverb), it translates to "as soon as", "scarcely", or "barely". It indicates that the second action (adiei a estreia) happened the exact moment the first action (os vi chorar) was completed.

Why is the infinitive chorar used instead of a continuous form like for "crying"?