An appositive renames the noun beside it. If the sentence still works without that rename, set it off with a pair of commas. Our captain, Lena Ortiz, called the play. The rename is extra. Comma pairs are one of the jobs in ACT comma rules.
Extra versus necessary
Lena Ortiz can come out and you still have a sentence about the captain. Commas on both sides. One comma and no closer is wrong.
If the rename is the only way to know which person, it is essential and takes no commas. My teammate Jordan brought the pencils can be essential when you have more than one teammate. The deletion test is the same one in essential and nonessential clauses.
Dashes do the same job, louder
Our captain — a former sprinter — stayed late. Dashes set off the rename when you want more emphasis. The dash rule is in dashes on ACT English. Punctuation overall is in ACT punctuation rules.
The bottom line
A rename you can delete gets two commas. A rename the sentence needs gets none.
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