Learn Spanish (Latin America): Se me cayeron las fichas al apostar.

In Spanish, dropping things is usually treated as an accident where the object acts on its own. The structure se me cayeron literally means "they fell from me." The se shows it was unintentional, me shows who was affected (you), and cayeron is the verb.

Why is the verb "cayeron" in the plural form if "I" dropped them?

In the accidental se construction, the person who experienced the accident (me) is the indirect object. The grammatical subject of the sentence is actually the thing that fell: las fichas (the chips). Because fichas is plural, the verb must be the plural cayeron.

The current lesson is about resulting states with "quedarse". How could I use that verb to describe the result of dropping these chips?

While this sentence focuses on the action of dropping them, you can describe the resulting state of being chip-less by using quedarse. For example, Me quedé sin fichas means "I was left without chips" or "I ran out of chips."

How does "al apostar" mean "when betting"?

Combining al (which is a + el) with an infinitive verb like apostar is a common Spanish shortcut. It translates to "upon doing something" or "when doing something." So, al apostar simply means "when betting" or "upon betting."